tag:theconversation.com,2011:/au/topics/gravitational-waves-9473/articlesGravitational waves – The Conversation2023-09-28T19:58:35Ztag:theconversation.com,2011:article/1802372023-09-28T19:58:35Z2023-09-28T19:58:35ZA search for links between two of the universe’s most spectacular phenomena has come up empty – for now<figure><img src="https://images.theconversation.com/files/550815/original/file-20230928-28-yfqf00.jpg?ixlib=rb-1.1.0&rect=0%2C4%2C3000%2C1679&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.anu.edu.au/news/all-news/scientists-detect-a-black-hole-swallowing-a-neutron-star">Carl Knox / OzGrav</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Every so often, astronomers glimpse an intense flash of radio waves from space – a flash that lasts only instants but puts out as much energy in a millisecond as the Sun does in a few years. The origin of these “fast radio bursts” is <a href="https://theconversation.com/535-new-fast-radio-bursts-help-answer-deep-questions-about-the-universe-and-shed-light-on-these-mysterious-cosmic-events-161976">one of the greatest mysteries</a> in astronomy today. </p>
<p>There is no shortage of ideas to explain the cause of the bursts: a <a href="https://frbtheorycat.org/index.php/Main_Page">catalogue</a> of current theories shows more than 50 potential scenarios. You can take your pick from highly magnetised neutron stars, collisions of incredibly dense stars or many more extreme or exotic phenomena. </p>
<p>How can we figure out which theory is correct? One way is to look for more information about the bursts, using other channels: specifically, using ripples in the fabric of the universe called gravitational waves.</p>
<p>In <a href="https://iopscience.iop.org/article/10.3847/1538-4357/acd770">a new study</a> published in The Astrophysical Journal, we cross-referenced dozens of fast radio burst observations with data from gravitational wave telescopes to see if we could find any links.</p>
<h2>Gravitational wave astronomy</h2>
<p>If you think of telescopes, you probably think of ones that look for <a href="https://imagine.gsfc.nasa.gov/science/toolbox/multiwavelength1.html">electromagnetic signals</a> such as light, radio waves or x-rays. Lots of stars and other things in the cosmos produce these signals. But dust and gas abundant in the galaxies in which star systems reside can dim or block these signals.</p>
<p>Gravitational waves are different: they pass straight through matter, so nothing can really get in their way.</p>
<figure class="align-center ">
<img alt="An illustration showing a neutron star and a black hole about to collide, with light swirling around them." src="https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/550822/original/file-20230928-29-kzxcm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Researchers looked for gravitational waves from colliding pairs of neutron stars, as well as those from neutron stars and black holes, around the time and sky position of known fast radio bursts.</span>
<span class="attribution"><a class="source" href="https://outreach.ozgrav.org/portal2/gallery/#GmediaGallery_2-albums-25-153">Carl Knox / OzGrav</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Astronomers have so far detected gravitational waves from colliding systems of compact stars such as <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">black holes</a> and <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">neutron stars</a>, as well as discovering the engines behind <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">gamma-ray bursts</a>.</p>
<p>We also have reason to think fast radio bursts may produce gravitational wave signals.</p>
<h2>What produces fast radio bursts?</h2>
<p>Some fast radio bursts have been seen to repeat, but most are seen as single events. </p>
<p>For the repeating bursts, a recent <a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">simultaneous observation</a> of x-rays and a radio burst from a highly magnetised neutron star in our own Milky Way galaxy proves this type of star can produce fast radio bursts. No source has so far been identified for the non-repeaters.</p>
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<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
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<p>However, some theories involve astronomical objects and events we know produce strong gravitational waves. So if we have an idea of where in the sky a fast radio burst occurs, and when, we can do a targeted, sensitive search for gravitational waves over the same patch of sky. </p>
<h2>The CHIME radio telescope</h2>
<p>To look for new evidence on what causes fast radio bursts I co-led a targeted search using fast radio bursts detected by a radio telescope called <a href="https://theconversation.com/535-new-fast-radio-bursts-help-answer-deep-questions-about-the-universe-and-shed-light-on-these-mysterious-cosmic-events-161976">CHIME</a> in Canada.</p>
<p>As the <a href="https://www.chime-frb.ca/">CHIME/FRB</a> project has detected hundreds of fast radio bursts, there’s a good chance of catching one close enough to Earth to be observed by a gravitational wave telescope. This is important as fast radio bursts are so bright they can be seen from billions of light years away – much farther than present gravitational wave observatories can see.</p>
<p>So what did we do and how did we do it? The project team gave us the data for a few hundred fast radio bursts. As much of this data is still not publicly available, we signed a special agreement that we would not share the details outside the search teams. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/535-new-fast-radio-bursts-help-answer-deep-questions-about-the-universe-and-shed-light-on-these-mysterious-cosmic-events-161976">535 new fast radio bursts help answer deep questions about the universe and shed light on these mysterious cosmic events</a>
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<p>We then estimated the distance to each fast radio burst, and searched for gravitational wave data around the 40 closest events (which had evidence of being within gravitational wave detector range).</p>
<p>Our search team was a small group of scientists from the LIGO gravitational wave observatory in the United States, the Virgo observatory in Italy, and collaborators from the fast radio burst team CHIME/FRB. </p>
<figure class="align-center ">
<img alt="A photo showing an array of radio antennas beneath a sunny sky." src="https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/550825/original/file-20230928-15-9i311a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The CHIME radio telescope has detected hundreds of fast radio bursts.</span>
<span class="attribution"><span class="source">The CHIME Collaboration</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We looked for gravitational wave signals around the sky position of each non-repeating fast radio burst around the time each occurred. For these non-repeaters, we did two kinds of search: one that looked for known gravitational wave signals, like those from colliding black holes or neutrons, and another that essentially looked for any burst of energy that was out of the ordinary.</p>
<p>For the repeating bursts, because we know that at least one such source is associated with a magnetised neutron star, we looked for the kind of gravitational wave signals we might expect from an isolated neutron star.</p>
<h2>What did we find out?</h2>
<p>Did we discover anything? Well, not this time. </p>
<p>It was not such a surprise, as we think fast radio bursts are much more common than detectable gravitational wave signals. In other words, gravitational wave sources would only account for a small fraction of fast radio bursts.</p>
<p>However, the closest fast radio burst in our sample was almost close enough for us to rule out the possibility it was caused by a collision between a neutron star and a black hole. Uncertainty in the distance to the burst means we can’t rule it out conclusively, but we are encourage by the fact the sensitive range of gravitational wave detectors is closing in on the distance to fast radio bursts.</p>
<h2>What next?</h2>
<p>Despite no definitive results this time, future searches could be a vital stepping stone to understanding fast radio bursts. </p>
<p>Gravitational wave detectors have become <a href="https://theconversation.com/gravitational-wave-detector-ligo-is-back-online-after-3-years-of-upgrades-how-the-worlds-most-sensitive-yardstick-reveals-secrets-of-the-universe-204339">more sensitive</a> than when we conducted this search, and will continue to improve in the coming years. This means they will allow a greater reach throughout the cosmos, so we can test a much larger sample of fast radio bursts. </p>
<p>We are also targeting future fast radio bursts from the known repeating source in our own galaxy mentioned above.</p>
<hr>
<p><em>Eric Howell would like to acknowledge the contribution towards this work by the other FRB-GW search co-chair Ryan Fisher; the other members of the paper writing team Kara Merfeld, Iara Tosta e Melo, Michael Patel; and the CHIME/FRB collaborators Shriharsh Tendulkar, Mohit Bhardwaj, Andrew Zwaniga, Adam Dong and Victoria Kaspi. The LIGO-Virgo GW analysts included Michael Patel, Patrick Sutton, Teresa Slaven-Blair, Amin Boumerdassi, Grace Johns, Nathan Ormsby, Max Elias Trevor, Adrian Helmling-Cornell, Hannah Griggs, Brandon Piotrzkowski, Benjamin Mannix, Kaemon Watada, Jacob Buchanan; the LIGO-Virgo review team were Tito Dal Canton, Marco Drag, Om Sharan Salafia, Ronaldas Macas and Michal Was.</em></p><img src="https://counter.theconversation.com/content/180237/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eric Howell does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Massive flashes of energy known as ‘fast radio bursts’ have puzzled astronomers for years – and a new search for links to gravitational waves has so far found no connection.Eric Howell, OzGrav Associate Investigator; Adjunct Research Fellow in Astrophysics, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2088152023-06-30T20:57:15Z2023-06-30T20:57:15ZA subtle symphony of ripples in spacetime – astronomers use dead stars to measure gravitational waves produced by ancient black holes<figure><img src="https://images.theconversation.com/files/535073/original/file-20230630-14361-kaueuz.jpg?ixlib=rb-1.1.0&rect=38%2C76%2C4547%2C2919&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes and other massive objects create ripples in spacetime when they merge.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/black-holes-illustration-royalty-free-illustration/1088377636?phrase=gravitational+waves&adppopup=true">Victor de Schwanburg/Science Photo Library via Getty Images</a></span></figcaption></figure><p>An international team of astronomers has detected a <a href="https://doi.org/10.3847/2041-8213/acdac6">faint signal</a> of gravitational waves reverberating through the universe. By using dead stars as a giant network of <a href="https://iopscience.iop.org/collections/apjl-230623-245-Focus-on-NANOGrav-15-year">gravitational wave detectors</a>, the collaboration – called <a href="https://nanograv.org/">NANOGrav</a> – was able to measure a low-frequency hum from a chorus of <a href="https://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">ripples of spacetime</a>.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies and has written about <a href="https://wwnorton.com/books/9780393343861">cosmology</a>, <a href="https://wwnorton.com/books/9780393357509">black holes</a> and <a href="https://www.penguinrandomhouse.com/books/718149/worlds-without-end-by-chris-impey/">exoplanets</a>. I’ve researched the <a href="https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/survey-of-agn-and-supermassive-black-holes-in-the-cosmos-survey/B1ADC49E96B9D865D55188EC839ED033">evolution of supermassive black holes</a> using the Hubble Space telescope.</p>
<p>Though members of the team behind this new discovery aren’t yet certain, they strongly suspect that the background hum of gravitational waves they measured was caused by countless ancient merging events of supermassive black holes.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zsDOqLWuWQ4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Pulsars are spinning dead stars that emit strong beams of radiation and can be used as accurate cosmic clocks.</span></figcaption>
</figure>
<h2>Using dead stars for cosmology</h2>
<p><a href="https://www.ligo.caltech.edu/page/what-are-gw">Gravitational waves</a> are ripples in spacetime caused by massive accelerating objects. Albert Einstein predicted their existence in his <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">general theory of relativity</a>, in which he hypothesized that when a gravitational wave passes through space, it makes the space shrink then expand periodically.</p>
<p>Researchers first detected direct evidence of gravitational waves in 2015, when the <a href="https://theconversation.com/gravitational-wave-detector-ligo-is-back-online-after-3-years-of-upgrades-how-the-worlds-most-sensitive-yardstick-reveals-secrets-of-the-universe-204339">Laser Interferometer Gravitational-Wave Observatory, known as LIGO</a>, <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">picked up a signal</a> from a <a href="https://www.ligo.caltech.edu/detection">pair of merging black holes</a> that had traveled 1.3 billion light-years to reach Earth.</p>
<p>The NANOGrav collaboration is also trying to detect spacetime ripples, but on an interstellar scale. The team <a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">used pulsars</a>, rapidly spinning dead stars that emit a beam of radio emissions. Pulsars are functionally similar to a lighthouse – as they spin, their beams can sweep across the Earth at <a href="https://nanograv.org/science/topics/pulsars-cosmic-clocks">regular intervals</a>.</p>
<p>The NANOGrav team used pulsars that <a href="https://doi.org/10.3847/2041-8213/acda9a">rotate incredibly fast</a> – up to 1,000 times per second – and these pulses can be timed like the ticking of an <a href="https://nanograv.org/science/topics/pulsars-cosmic-clocks">extremely accurate cosmic clock</a>. As gravitational waves sweep past a pulsar at the speed of light, the waves will very slightly expand and contract the distance between the pulsar and the Earth, ever so slightly changing the time between the ticks. </p>
<p>Pulsars are such accurate clocks that it is possible to measure their ticking with an accuracy to within 100 nanoseconds. That lets astronomers calculate the distance between a pulsar and Earth to within <a href="https://astronomy.swin.edu.au/cosmos/p/Pulsar+Timing">100 feet</a> (30 meters). Gravitational waves change the distance between these pulsars and Earth by tens of miles, making pulsars easily sensitive enough to detect this effect.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A giant, white reflecting dish with a receiver." src="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The NANOGrav team used a number of radio telescopes, including the Green Bank Telescope in West Virginia, to listen to pulsars for 15 years.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/gallery/green-bank-telescope/">NRAO/AUI/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Finding a hum within cacophony</h2>
<p>The first thing the NANOGrav team had to do was control for the <a href="https://doi.org/10.3847/2041-8213/acda88">noise in its cosmic gravitational wave detector</a>. This included <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">noise in the radio receivers</a> it used and subtle astrophysics that affect the behavior of pulsars. Even accounting for these effects, the team’s approach was not sensitive enough to detect gravitational waves from <a href="https://doi.org/10.48550/arXiv.2306.16222">individual supermassive black hole binaries</a>. However, it had enough sensitivity to detect the sum of all the massive black hole mergers that have occurred anywhere in the universe since the Big Bang – as many as a million overlapping signals.</p>
<p>In a musical analogy, it is like standing in a busy downtown and hearing the faint sound of a symphony somewhere in the distance. You can’t pick out a single instrument because of the noise of the cars and the people around you, but you can hear the hum of a hundred instruments. The team had to tease out the signature of this <a href="https://www.space.com/gravitational-wave-background-universe-1st-detection">gravitational wave “background”</a> from other competing signals.</p>
<p>The team was able to detect this symphony by measuring a network of 67 different pulsars for 15 years. If some disruption in the ticking of one pulsar was due to gravitational waves from the distant universe, all the pulsars the team was watching would be affected in a similar way. On June 28, 2023, the team published <a href="https://www.nytimes.com/2023/06/28/science/astronomy-gravitational-waves-nanograv.html">four papers</a> describing its project and the evidence it found of the gravitational wave background.</p>
<p>The hum the NANOGrav collaboration found is produced from the merging of black holes that are billions of times more massive than the Sun. These black holes spin around one another very slowly and produce gravitational waves with <a href="https://www.scienceinschool.org/article/2017/gravitational-waves-taxonomy/">frequencies of one-billionth of a hertz</a>. That means the spacetime ripples have an oscillation every few decades. This slow oscillation of the wave is the reason the team needed to rely on the incredibly accurate timekeeping of pulsars.</p>
<p>These gravitational waves are different from <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">the waves LIGO can detect</a>. LIGO’s signals are produced when two black holes <a href="https://media.ligo.northwestern.edu/gallery/mass-plot">10 to 100 times the mass of the Sun</a> merge into one rapidly spinning object, creating gravitational waves that oscillate hundreds of times per second.</p>
<p>If you think of black holes as a tuning fork, the smaller the event, the faster the tuning fork vibrates and the higher the pitch. LIGO detects gravitational waves that “ring” in the audible range. The black hole mergers the NANOGrav team has found “ring” with a frequency billions of times too low to hear. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star-filled sky with many spiral galaxies." src="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=610&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=610&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=610&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=767&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=767&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=767&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The James Webb Space Telescope has allowed astronomers to peer back in time and study the first galaxies to form after the Big Bang.</span>
<span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1">NASA, ESA, CSA, STScI</a></span>
</figcaption>
</figure>
<h2>Giant black holes in the early universe</h2>
<p>Astronomers have long been interested in <a href="https://theconversation.com/james-webb-space-telescope-an-astronomer-explains-the-stunning-newly-released-first-images-186800">studying how stars and galaxies first emerged</a> in the aftermath of the Big Bang. This new finding from the NANOGrav team is like adding another color – gravitational waves – to the picture of the early universe that is just starting to emerge, in large part thanks to <a href="https://theconversation.com/the-james-webb-space-telescope-is-finally-ready-to-do-science-and-its-seeing-the-universe-more-clearly-than-even-its-own-engineers-hoped-for-184989">the James Webb Space Telescope</a>.</p>
<p>A major scientific goal of the <a href="https://webbtelescope.org/home">James Webb Space Telescope</a> is to help researchers study how the first stars and galaxies formed after the Big Bang. To do this, James Webb was designed to detect the faint light from incredibly distant stars and galaxies. The farther away an object is, the longer it takes the light to get to Earth, so James Webb is effectively a time machine that can peer back over 13.5 billion years to see light from the <a href="https://webb.nasa.gov/content/science/firstLight.html">first stars and galaxies</a> in the universe. </p>
<p>It has been very successful in the quest, having found <a href="https://www.space.com/james-webb-space-telescope-galaxies-early-universe-first-light">hundreds of galaxies</a> that flooded the universe with light in the first 700 million years after the big bang. The telescope has also detected the <a href="https://www.livescience.com/james-webb-space-telescope-discovers-oldest-black-hole-in-the-universe-a-cosmic-monster-ten-million-times-heavier-than-the-sun">oldest black hole</a> in the universe, located at the center of a galaxy that formed just 500 million years after the Big Bang.</p>
<p>These findings are challenging existing theories of the evolution of the universe. </p>
<p>It takes a long time to <a href="https://www.smithsonianmag.com/smart-news/webb-telescope-finds-evidence-of-massive-galaxies-that-defy-theories-of-the-early-universe-180981689/">grow a massive galaxy</a>. Astronomers know that supermassive black holes <a href="https://theconversation.com/say-hello-to-sagittarius-a-the-black-hole-at-the-center-of-the-milky-way-galaxy-183008">lie at the center of every galaxy</a> and have mass proportional to their host galaxies. So these ancient galaxies almost certainly have <a href="https://ec.europa.eu/research-and-innovation/en/horizon-magazine/how-did-supermassive-black-holes-grow-so-fast">the correspondingly massive black hole</a> in their centers.</p>
<p>The problem is that the objects James Webb has been finding are far bigger than current theory says they should be. </p>
<p>These new results from the NANOGrav team emerged from astronomers’ first opportunity to listen to the gravitational waves of the ancient universe. The findings, while tantalizing, <a href="https://doi.org/10.1038/d41586-023-02167-7">aren’t quite strong enough to claim a definitive discovery</a>. That will likely change, as the team has expanded its pulsar network <a href="https://nanograv.org/news/15yrRelease">to include 115 pulsars</a> and should get results from this next survey around 2025. As James Webb and other research challenges existing theories of how galaxies evolved, the ability to study the era after the Big Bang using gravitational waves could be an invaluable tool.</p><img src="https://counter.theconversation.com/content/208815/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation.</span></em></p>Astronomers have for the first time detected the background hum of gravitational waves likely caused by merging black holes.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2084842023-06-29T00:13:09Z2023-06-29T00:13:09ZUsing a detector the size of a galaxy, astronomers find strongest evidence yet for gravitational waves from supermassive black hole pairs<figure><img src="https://images.theconversation.com/files/534245/original/file-20230627-24-e1bn10.png?ixlib=rb-1.1.0&rect=0%2C10%2C3456%2C1929&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">OzGrav / Swinburne / Carl Knox</span></span></figcaption></figure><p>When black holes and other enormously massive, dense objects whirl around one another, they send out ripples in space and time called <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">gravitational waves</a>. These waves are one of the few ways we have to study the enigmatic cosmic giants that create them.</p>
<p>Astronomers have observed the high-frequency “chirps” of colliding black holes, but the ultra-low-frequency rumble of supermassive black holes orbiting one another has proven harder to detect. For decades, we have been observing <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">pulsars</a>, a type of star that pulses like a lighthouse, in search of the faint rippling of these waves.</p>
<p>Today, pulsar research collaborations around the world – including ours, the <a href="https://www.atnf.csiro.au/research/pulsar/ppta/">Parkes Pulsar Timing Array</a> – announced their <a href="https://doi.org/10.3847/2041-8213/acdd02">strongest evidence yet</a> for the existence of these waves.</p>
<h2>What are gravitational waves?</h2>
<p>In 1915, German-born physicist Albert Einstein presented a breakthrough insight into the nature of <a href="https://theconversation.com/explainer-gravity-5256">gravity</a>: the general theory of relativity.</p>
<p>The theory describes the Universe as a four-dimensional “fabric” called spacetime that can stretch, squeeze, bend and twist. Massive objects distort this fabric to give rise to gravity.</p>
<p>A curious consequence of the theory is that the motion of massive objects should produce ripples in this fabric, called gravitational waves, which spread at the speed of light.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-gravity-5256">Explainer: gravity</a>
</strong>
</em>
</p>
<hr>
<p>It takes an enormous amount of energy to create the tiniest of these ripples. For this reason, Einstein was convinced gravitational waves would never be directly observed. </p>
<p>A century later, researchers from the LIGO and Virgo collaborations witnessed the <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">collision of two black holes</a>, which sent a burst of gravitational waves <a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">chirping</a> throughout the Universe.</p>
<p>Now, seven years after this discovery, radio astronomers from Australia, China, Europe, India, and North America have found evidence for ultra-low-frequency gravitational waves.</p>
<h2>A slow rumbling of gravitational waves</h2>
<p>Unlike the sudden burst of gravitational waves reported in 2016, these ultra-low-frequency gravitational waves take years or even decades to oscillate. </p>
<p>They are expected to be produced by <a href="https://theconversation.com/when-galaxies-collide-the-growth-of-supermassive-black-holes-19321">pairs of supermassive black holes</a>, orbiting at the cores of distant galaxies throughout the Universe. To find these gravitational waves, scientists would need to construct a detector the size of a galaxy. </p>
<figure class="align-center ">
<img alt="An illustration showing Earth, pulsars, and gravitational waves." src="https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">As gravitational waves warp spacetime around Earth, they distort the arrival times of radio waves from distant pulsars.</span>
<span class="attribution"><span class="source">OzGrav / Swinburne / Carl Knox</span></span>
</figcaption>
</figure>
<p>Or we can use pulsars, which are already spread across the galaxy, and whose pulses arrive at our telescopes with the regularity of precise clocks.</p>
<p>CSIRO’s Parkes radio telescope, <a href="https://blog.csiro.au/parkes-telescope-indigenous-name/">Murriyang</a>, has been observing an array of these pulsars for almost two decades. Our <a href="https://www.atnf.csiro.au/research/pulsar/ppta/">Parkes Pulsar Timing Array</a> team is one of several collaborations around the world that have <a href="https://doi.org/10.3847/2041-8213/acdd02">today announced</a> hints of gravitational waves in their latest data sets. </p>
<p>Other collaborations in China (CPTA), Europe and India (EPTA and InPTA), and North America (NANOGrav) see similar signals.</p>
<p>The signal we are searching for is a random “ocean” of gravitational waves produced by all the pairs of supermassive black holes in the Universe. </p>
<p>Observing these waves is not only another triumph of Einstein’s theory, but has important consequences for our understanding of the history of galaxies in the Universe. Supermassive black holes are the engines at the heart of galaxies that feed on gas and regulate star formation.</p>
<p>The signal appears as a low-frequency rumble, common to all pulsars in the array. As the gravitational waves wash over Earth, they affect the apparent rotation rates of the pulsars.</p>
<p>The stretching and squeezing of our galaxy by these waves ultimately changes the distances to the pulsars by just tens of metres. That’s not much when the pulsars are typically about 1,000 light-years away (that’s about 10,000,000,000,000,000,000 metres).</p>
<p>Remarkably, we can observe these shifts in spacetime as nanosecond delays to the pulses, which radio astronomers can track with relative ease because pulsars are such stable natural clocks.</p>
<h2>What has been announced?</h2>
<p>Because the ultra-low-frequency gravitational waves take years to oscillate, the signal is expected to emerge slowly. </p>
<p>First, radio astronomers observed a <a href="https://doi.org/10.3847/2041-8213/abd401">common rumble</a> in the pulsars, but its origin was unknown. </p>
<p>Now, the unique fingerprint of gravitational waves is beginning to appear as an attribute of this signal, observed by each of the pulsar timing array collaborations around the world. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-galaxies-collide-the-growth-of-supermassive-black-holes-19321">When galaxies collide: the growth of supermassive black holes</a>
</strong>
</em>
</p>
<hr>
<p>This fingerprint describes a particular relationship between the similarity of pulse delays and the separation angle between pulsar pairs on the sky. </p>
<p>The relationship arises because spacetime at Earth is stretched, changing the distances to pulsars in a way that depends on their direction. Pulsars close together in the sky show a more similar signal than pulsars separated at right angles, for example.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">CSIRO’s Parkes radio telescope, Murriyang.</span>
<span class="attribution"><span class="source">CSIRO / A. Cherney</span></span>
</figcaption>
</figure>
<p>The breakthrough has been enabled by improved technology at our observatories. The Parkes Pulsar Timing Array has the longest high-quality data set, thanks to the advanced receiver and signal processing technology installed on Murriyang. This technology has enabled the telescope to discover many of the best pulsars used by collaborations around the globe for the gravitational wave searches.</p>
<p>Earlier results from our collaboration and others showed the signal expected from gravitational waves <a href="https://theconversation.com/where-are-the-missing-gravitational-waves-47940">was missing from pulsar observations</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/where-are-the-missing-gravitational-waves-47940">Where are the missing gravitational waves?</a>
</strong>
</em>
</p>
<hr>
<p>Now, we seem to be seeing the signal with relative clarity. By segmenting our long data set into shorter “time-slices”, we show the signal appears to be growing with time. The underlying cause of this observation is unknown, but it may be that the gravitational waves are behaving unexpectedly.</p>
<p>The new evidence for ultra-low-frequency gravitational waves is exciting for astronomers. To confirm these signatures, the global collaborations will need to combine their data sets, which increases their sensitivity to gravitational waves many-fold. </p>
<p>Efforts to produce this combined data set are now in progress under the <a href="https://ipta4gw.org/">International Pulsar Timing Array</a> project, whose members met in Port Douglas in Far North Queensland last week. Future observatories, like the Square Kilometre Array under construction in Australia and South Africa, will turn these studies into a rich source of knowledge about the history of our Universe.</p><img src="https://counter.theconversation.com/content/208484/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>By timing radio pulses from an array of galactic pulsars, scientists see hints of gravitational waves from supermassive black hole pairs in a breakthrough that may reveal hidden details of galaxy evolution.Daniel Reardon, Postdoctoral researcher in pulsar timing and gravitational waves, Swinburne University of TechnologyAndrew Zic, Research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2043392023-05-22T12:27:17Z2023-05-22T12:27:17ZGravitational wave detector LIGO is back online after 3 years of upgrades – how the world’s most sensitive yardstick reveals secrets of the universe<figure><img src="https://images.theconversation.com/files/527292/original/file-20230519-29-jhi1qv.jpg?ixlib=rb-1.1.0&rect=335%2C178%2C6276%2C2651&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When two massive objects – like black holes or neutron stars – merge, they warp space and time. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/gravitational-waves-illustration-royalty-free-illustration/685026451?phrase=gravitational+waves&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>After a three-year hiatus, scientists in the U.S. have just turned on detectors capable of <a href="https://observing.docs.ligo.org/plan/">measuring gravitational waves</a> – tiny ripples in space itself that travel through the universe. </p>
<p>Unlike light waves, gravitational waves are nearly <a href="https://www.ligo.caltech.edu/page/why-detect-gw">unimpeded by the galaxies, stars, gas and dust</a> that fill the universe. This means that by measuring gravitational waves, <a href="https://scholar.google.com/citations?user=33fO9GoAAAAJ&hl=en&oi=sra">astrophysicists like me</a> can peek directly into the heart of some of these most spectacular phenomena in the universe. </p>
<p>Since 2020, the Laser Interferometric Gravitational-Wave Observatory – commonly known as <a href="https://www.ligo.caltech.edu">LIGO</a> – has been sitting dormant while it underwent some exciting upgrades. These improvements will <a href="https://doi.org/10.1103/PhysRevX.13.011048">significantly boost the sensitivity</a> of LIGO and should allow the facility to observe more-distant objects that produce smaller ripples in <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">spacetime</a>.</p>
<p>By detecting more events that create gravitational waves, there will be more opportunities for astronomers to also observe the light produced by those same events. Seeing an event <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">through multiple channels of information</a>, an approach called <a href="https://doi.org/10.1038/s42254-019-0101-z">multi-messenger astronomy</a>, provides astronomers <a href="https://doi.org/10.3847/2041-8213/aa91c9">rare and coveted opportunities</a> to learn about physics far beyond the realm of any laboratory testing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Sun and Earth warping space." src="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">According to Einstein’s theory of general relativity, massive objects warp space around them.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/gravity-and-general-theory-of-relativity-concept-royalty-free-image/923504630?phrase=gravity+general+relativity&adppopup=true">vchal/iStock via Getty Images</a></span>
</figcaption>
</figure>
<h2>Ripples in spacetime</h2>
<p>According to <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">Einstein’s theory of general relativity</a>, mass and energy warp the shape of space and time. The bending of spacetime determines how objects move in relation to one another – what people experience as gravity. </p>
<p>Gravitational waves are created when massive objects like black holes or neutron stars merge with one another, producing sudden, large changes in space. The process of space warping and flexing sends ripples across the universe like a <a href="https://www.ligo.caltech.edu/page/what-are-gw">wave across a still pond</a>. These waves travel out in all directions from a disturbance, minutely bending space as they do so and ever so slightly changing the distance between objects in their way. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_C5Bl_hE8fM?wmode=transparent&start=17" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">When two massive objects – like a black hole or a neutron star – get close together, they rapidly spin around each other and produce gravitational waves. The sound in this NASA visualization represents the frequency of the gravitational waves.</span></figcaption>
</figure>
<p>Even though the astronomical events that produce gravitational waves involve some of the most massive objects in the universe, the stretching and contracting of space is infinitesimally small. A strong gravitational wave passing through the Milky Way may only change the diameter of the entire galaxy by three feet (one meter).</p>
<h2>The first gravitational wave observations</h2>
<p>Though first predicted by Einstein in 1916, scientists of that era had little hope of measuring the tiny changes in distance postulated by the theory of gravitational waves.</p>
<p>Around the year 2000, scientists at Caltech, the Massachusetts Institute of Technology and other universities around the world finished constructing what is essentially the most precise ruler ever built – the <a href="https://doi.org/10.1088/0034-4885/72/7/076901">LIGO observatory</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An L-shaped facility with two long arms extending out from a central building." src="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The LIGO detector in Hanford, Wash., uses lasers to measure the minuscule stretching of space caused by a gravitational wave.</span>
<span class="attribution"><a class="source" href="https://www.ligo.org/multimedia/gallery/lho-images/Aerial5.jpg">LIGO Laboratory</a></span>
</figcaption>
</figure>
<p><a href="https://www.ligo.caltech.edu/page/what-is-ligo">LIGO is comprised of two separate observatories</a>, with one located in Hanford, Washington, and the other in Livingston, Louisiana. Each observatory is shaped like a giant L with two, 2.5-mile-long (four-kilometer-long) arms extending out from the center of the facility at 90 degrees to each other.</p>
<p>To measure gravitational waves, researchers shine a laser from the center of the facility to the base of the L. There, the laser is split so that a beam travels down each arm, reflects off a mirror and returns to the base. If a gravitational wave passes through the arms while the laser is shining, the two beams will return to the center at ever so slightly different times. By measuring this difference, physicists can discern that a gravitational wave passed through the facility.</p>
<p><a href="https://doi.org/10.1088/0034-4885/72/7/076901">LIGO began operating</a> in the early 2000s, but it was not sensitive enough to detect gravitational waves. So, in 2010, the LIGO team temporarily shut down the facility to perform <a href="https://doi.org/10.1088/0264-9381/32/7/074001">upgrades to boost sensitivity</a>. The upgraded version of LIGO started <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">collecting data in 2015 and almost immediately</a> <a href="https://doi.org/10.1103/PhysRevLett.116.061102">detected gravitational waves</a> produced from the merger of two black holes. </p>
<p>Since 2015, LIGO has completed <a href="https://observing.docs.ligo.org/plan/#timeline">three observation runs</a>. The first, run O1, lasted about four months; the second, O2, about nine months; and the third, O3, ran for 11 months before the COVID-19 pandemic forced the facilities to close. Starting with run O2, LIGO has been jointly observing with an <a href="https://doi.org/10.1088/0264-9381/32/2/024001">Italian observatory called Virgo</a>.</p>
<p>Between each run, scientists improved the physical components of the detectors and data analysis methods. By the end of run O3 in March 2020, researchers in the LIGO and Virgo collaboration had detected <a href="https://doi.org/10.48550/arXiv.2111.03606">about 90 gravitational waves</a> from the merging of black holes and neutron stars.</p>
<p>The observatories have still <a href="https://dcc.ligo.org/LIGO-P1200087/public">not yet achieved their maximum design sensitivity</a>. So, in 2020, both observatories shut down for upgrades <a href="https://www.ligo.caltech.edu/news/ligo20200326">yet again</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two people in white lab outfits working on complicated machinery." src="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Upgrades to the mechanical equipment and data processing algorithms should allow LIGO to detect fainter gravitational waves than in the past.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/image/ligo20190326b">LIGO/Caltech/MIT/Jeff Kissel</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Making some upgrades</h2>
<p>Scientists have been working on <a href="https://dcc-llo.ligo.org/public/0182/G2200736/001/UpdateonLVKDetectors.pdf">many technological improvements</a>.</p>
<p>One particularly promising upgrade involved adding a 1,000-foot (300-meter) <a href="https://spie.org/news/photonics-focus/marapr-2023/squeezing-light-for-ligo?SSO=1">optical cavity</a> to improve a <a href="https://doi.org/10.1088/1361-6633/aab906">technique called squeezing</a>. Squeezing allows scientists to reduce detector noise using the quantum properties of light. With this upgrade, the LIGO team should be able to detect much weaker gravitational waves than before.</p>
<p><a href="https://igc.psu.edu/people/bio/crh184/#nav-members">My teammates and I</a> are data scientists in the LIGO collaboration, and we have been working on a number of different upgrades to <a href="https://doi.org/10.48550/arXiv.2305.05625">software used to process LIGO data</a> and the algorithms that recognize <a href="https://doi.org/10.48550/arXiv.2305.06286">signs of gravitational waves in that data</a>. These algorithms function by searching for patterns that match <a href="https://doi.org/10.48550/arXiv.2211.16674">theoretical models of millions</a> of possible black hole and neutron star merger events. The improved algorithm should be able to more easily pick out the faint signs of gravitational waves from background noise in the data than the previous versions of the algorithms.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A GIF showing a star brightening over a few days." src="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=641&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=641&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=641&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=805&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=805&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=805&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronomers have captured both the gravitational waves and light produced by a single event, the merger of two neutron stars. The change in light can be seen over the course of a few days in the top right inset.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/press-release/nasa-missions-catch-first-light-from-a-gravitational-wave-event">Hubble Space Telescope, NASA and ESA</a></span>
</figcaption>
</figure>
<h2>A hi-def era of astronomy</h2>
<p>In early May 2023, LIGO began a short test run – called an engineering run – to make sure everything was working. On May 18, LIGO detected gravitational waves likely <a href="https://gcn.nasa.gov/circulars/33813">produced from a neutron star merging into a black hole</a>.</p>
<p>LIGO’s 20-month observation run 04 will officially <a href="https://www.ligo.org/news/images/ER15-newsitem.pdf">start on May 24,</a> and it will later be joined by Virgo and a new Japanese observatory – the Kamioka Gravitational Wave Detector, or KAGRA. </p>
<p>While there are many scientific goals for this run, there is a particular focus on detecting and localizing gravitational waves in real time. If the team can identify a gravitational wave event, figure out where the waves came from and alert other astronomers to these discoveries quickly, it would enable astronomers to point other telescopes that collect visible light, radio waves or other types of data at the source of the gravitational wave. Collecting multiple channels of information on a single event – <a href="https://doi.org/10.3847/1538-4357/ab0e8f">multi-messenger astrophysics</a> – is like adding color and sound to a black-and-white silent film and can provide a much deeper understanding of astrophysical phenomena.</p>
<p>Astronomers have only observed a single event <a href="https://doi.org/10.3847/2041-8213/aa91c9">in both gravitational waves and visible light</a> to date – the merger of <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">two neutron stars seen in 2017</a>. But from this single event, physicists were able to study the <a href="https://doi.org/10.1038/nature24471">expansion of the universe</a> and confirm the origin of some of the universe’s most energetic events known as <a href="https://doi.org/10.3847/2041-8213/aa920c">gamma-ray bursts</a>.</p>
<p>With run O4, astronomers will have access to the most sensitive gravitational wave observatories in history and hopefully will collect more data than ever before. My colleagues and I are hopeful that the coming months will result in one – or perhaps many – multi-messenger observations that will push the boundaries of modern astrophysics.</p><img src="https://counter.theconversation.com/content/204339/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chad Hanna receives funding from the National Science Foundation and NASA.</span></em></p>Upgrades to the hardware and software of the advanced observatory should allow astrophysicists to detect much fainter gravitational waves than before.Chad Hanna, Professor of Physics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2023412023-03-27T19:00:47Z2023-03-27T19:00:47ZFor the first time, astronomers have linked a mysterious fast radio burst with gravitational waves<figure><img src="https://images.theconversation.com/files/517532/original/file-20230327-14-a7i9er.jpeg?ixlib=rb-1.1.0&rect=92%2C58%2C3138%2C1886&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ASKAP.</span> <span class="attribution"><span class="source">CSIRO</span></span></figcaption></figure><p>We have <a href="https://www.nature.com/articles/s41550-023-01917-x">just published evidence</a> in Nature Astronomy for what might be producing mysterious bursts of radio waves coming from distant galaxies, known as <a href="https://theconversation.com/fast-radio-bursts-new-intergalactic-messengers-15700">fast radio bursts</a> or FRBs.</p>
<p>Two colliding <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341#:%7E:text=Origin%20of%20a%20neutron%20star&text=Once%20its%20nuclear%20fuel%20is,the%20mass%20of%20our%20sun.">neutron stars</a> – each the super-dense core of an exploded star – produced a burst of gravitational waves when they merged into a “<a href="https://www.ozgrav.org/news/research-highlight-the-aftermath-of-binary-neutron-star-mergers">supramassive” neutron star</a>. We found that two and a half hours later they produced an FRB when the neutron star collapsed into a black hole.</p>
<p>Or so we think. The key piece of evidence that would confirm or refute our theory – an optical or gamma-ray flash coming from the direction of the fast radio burst – vanished almost four years ago. In a few months, we might get another chance to find out if we are correct.</p>
<h2>Brief and powerful</h2>
<p>FRBs are incredibly powerful pulses of radio waves from space lasting about a thousandth of a second. Using data from a radio telescope in Australia, the Australian Square Kilometre Array Pathfinder (<a href="https://www.csiro.au/ASKAP">ASKAP</a>), <a href="https://www.science.org/doi/10.1126/science.aaw5903">astronomers have found</a> that most FRBs come from galaxies so distant, light takes <a href="https://theconversation.com/how-we-closed-in-on-the-location-of-a-fast-radio-burst-in-a-galaxy-far-far-away-119177">billions of years to reach us</a>. But what produces these radio wave bursts has been puzzling astronomers since <a href="https://www.science.org/doi/10.1126/science.1147532">an initial detection</a> in 2007.</p>
<p>The best clue comes from an object in our galaxy known as SGR 1935+2154. It’s a <a href="https://earthsky.org/space/what-is-a-magnetar/">magnetar</a>, which is a neutron star with magnetic fields about a trillion times stronger than a fridge magnet. On April 28 2020, it produced a <a href="https://www.nature.com/articles/s41586-020-2872-x">violent burst of radio waves</a> – similar to an FRB, although less powerful.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
</strong>
</em>
</p>
<hr>
<p>Astronomers have long predicted that two neutron stars – a binary – merging to produce a <a href="https://theconversation.com/explainer-black-holes-7431">black hole</a> should also produce a burst of radio waves. The two neutron stars will be highly magnetic, and black holes cannot have magnetic fields. <a href="https://www.aanda.org/articles/aa/full_html/2014/02/aa21996-13/aa21996-13.html">The idea</a> is the sudden vanishing of magnetic fields when the neutron stars merge and collapse to a black hole produces a fast radio burst. Changing magnetic fields produce electric fields – it’s how most power stations produce electricity. And the huge change in magnetic fields at the time of collapse could produce the intense electromagnetic fields of an FRB.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black field with two illustrations of galaxies in the foreground, and a yellow beam connecting them" src="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s impression of a fast radio burst traveling through space and reaching Earth.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1915a/">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The search for the smoking gun</h2>
<p>To test this idea, Alexandra Moroianu, a masters student at the University of Western Australia, looked for merging neutron stars detected by the Laser Interferometer Gravitational-Wave Observatory (<a href="https://www.ligo.org/index.php">LIGO</a>) in the US. The gravitational waves LIGO searches for are ripples in spacetime, produced by the collisions of two massive objects, such as neutron stars.</p>
<p>LIGO has found two binary neutron star mergers. Crucially, the second, known as <a href="https://www.ligo.org/detections/GW190425.php">GW190425</a>, occurred when a new FRB-hunting telescope called <a href="https://chime-experiment.ca/en">CHIME</a> was also operational. However, being new, it took CHIME two years <a href="https://theconversation.com/535-new-fast-radio-bursts-help-answer-deep-questions-about-the-universe-and-shed-light-on-these-mysterious-cosmic-events-161976">to release its first batch of data</a>. When it did so, Moroianu quickly identified a fast radio burst called <a href="https://www.chime-frb.ca/catalog/FRB20190425A">FRB 20190425A</a> which occurred only two and a half hours after GW190425.</p>
<p>Exciting as this was, there was a problem – only one of LIGO’s two detectors was working at the time, making it <a href="https://theconversation.com/weve-detected-new-gravitational-waves-we-just-dont-know-where-they-come-from-yet-116267">very uncertain</a> where exactly GW190425 had come from. In fact, there was a 5% chance this could just be a coincidence.</p>
<p>Worse, the <a href="https://fermi.gsfc.nasa.gov/">Fermi</a> satellite, which could have detected gamma rays from the merger – the “smoking gun” confirming the origin of GW190425 – was <a href="https://link.springer.com/article/10.1134/S1063773719110057">blocked by Earth</a> at the time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A nighttime view of white curved pipes arranged in a grid pattern" src="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">CHIME, the Canadian Hydrogen Intensity Mapping Experiment, has turned out to be uniquely suited to detecting FRBs.</span>
<span class="attribution"><span class="source">Andre Renard/Dunlap Institute/CHIME Collaboration</span></span>
</figcaption>
</figure>
<h2>Unlikely to be a coincidence</h2>
<p>However, the critical clue was that FRBs trace the total amount of gas they have passed through. We know this because high-frequency radio waves travel faster through the gas than low-frequency waves, so the time difference between them tells us the amount of gas.</p>
<p>Because we know the <a href="https://theconversation.com/half-the-matter-in-the-universe-was-missing-we-found-it-hiding-in-the-cosmos-138569">average gas density of the universe</a>, we can relate this gas content to distance, which is known as the <a href="https://www.nature.com/articles/s41586-020-2300-2">Macquart relation</a>. And the distance travelled by FRB 20190425A was a near-perfect match for the distance to GW190425. Bingo!</p>
<p>So have we discovered the source of all FRBs? No. There are not enough merging neutron stars in the Universe to explain the number of FRBs – some must still come from magnetars, like SGR 1935+2154 did.</p>
<p>And even with all the evidence, there’s still a one in 200 chance this could all be a giant coincidence. However, LIGO and two other gravitational wave detectors, <a href="https://www.virgo-gw.eu/">Virgo</a> and <a href="https://gwcenter.icrr.u-tokyo.ac.jp/en/">KAGRA</a>, will <a href="https://www.ligo.caltech.edu/page/observing-plans">turn back on</a> in May this year, and be more sensitive than ever, while CHIME and <a href="https://www.mwatelescope.org/">other radio telescopes</a> are ready to immediately detect any FRBs from neutron star mergers.</p>
<p>In a few months, we may find out if we’ve made a key breakthrough – or if it was just a flash in the pan.</p>
<hr>
<p><em>Clancy W. James would like to acknowledge Alexandra Moroianu, the lead author of the study; his co-authors, Linqing Wen, Fiona Panther, Manoj Kovalem (University of Western Australia), Bing Zhang and Shunke Ai (University of Nevada); and his late mentor, Jean-Pierre Macquart, who experimentally verified the gas-distance relation, which is now named after him.</em></p><img src="https://counter.theconversation.com/content/202341/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clancy William James receives funding from the Australian Research Council. </span></em></p>For years, astronomers have been detecting incredibly powerful pulses from the cosmos, without a confirmed source. Recent advances in astronomy are getting us closer to the solution.Clancy William James, Senior Lecturer (astronomy and astroparticle physics), Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1874192022-07-25T12:10:30Z2022-07-25T12:10:30ZAstronomers have found an especially sneaky black hole – discovery sheds light on star death, black hole formation and gravitational waves<figure><img src="https://images.theconversation.com/files/475698/original/file-20220722-23-alpuwz.jpg?ixlib=rb-1.1.0&rect=8%2C16%2C747%2C419&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">VFTS 243 is a binary system of a large, hot blue star and a black hole orbiting each other, as seen in this animation.</span> <span class="attribution"><a class="source" href="https://www.eso.org/public/videos/eso2210b/">ESO/L.Calçada</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>There is always something new and exciting happening in the field of black hole research. </p>
<p>Albert Einstein first published his book explaining <a href="https://doi.org/10.1007/978-94-011-6022-3_3">the theory of general relativity</a> – which postulated black holes – in 1922. One hundred years later, astronomers captured actual <a href="https://eventhorizontelescope.org/blog/astronomers-reveal-first-image-black-hole-heart-our-galaxy">images of the black hole at the center of the Milky Way</a>. In a recent paper, a team of astronomers describes another exciting new discovery: the <a href="https://doi.org/10.1038/s41550-022-01730-y">first “dormant” black hole</a> observed outside of the galaxy.</p>
<p><a href="http://www.idanginsburg.com">I am an astrophysicist</a> who has studied black holes – the most dense objects in the universe – for nearly two decades. Dormant black holes are black holes that do not emit any detectable light. Thus, they are notoriously difficult to find. This new discovery is exciting because it provides insight into the formation and evolution of black holes. This information is vital for understanding <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">gravitational waves</a> as well as other astronomical events. </p>
<h2>What exactly is VFTS 243?</h2>
<p>VFTS 243 is a binary system, meaning it is composed of two objects that orbit a common center of mass. The first object is a <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Starlog/staspe.html">very hot, blue star</a> with 25 times the mass of the Sun, and the second a black hole nine times more massive than the Sun. VFTS 243 is located in the Tarantula Nebula within the Large Magellanic Cloud, a satellite galaxy of the Milky Way located <a href="https://doi.org/10.1038/s41586-019-0999-4">about 163,000 light-years from Earth</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/J7P27gDVoGI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This video begins with a view of the Milky Way and zooms all the way to VFTS 243, which is located in the Large Magellanic Cloud.</span></figcaption>
</figure>
<p>The black hole in VFTS 243 is considered dormant because it is not emitting any detectable radiation. This is in stark contrast to other binary systems in which <a href="https://doi.org/10.1007/978-3-319-21846-5_111">strong X-rays are detected</a> from the black hole.</p>
<p>The black hole has a diameter of around 33 miles (54 kilometers) and is dwarfed by the energetic star, which is some 200,000 times larger. Both rapidly rotate around a common center of mass. Even with the most powerful telescopes, visually the system appears to be a single blue dot.</p>
<h2>Finding dormant black holes</h2>
<p>Astronomers suspect there are hundreds of such binary systems with black holes that do not emit X-rays hiding in the Milky Way and the Large Magellanic Cloud. Black holes are most easily visible when they are <a href="https://astrobites.org/2021/07/08/tidal-tugs-shed-light-on-binary-companions/">stripping matter from a companion star</a>, a process known as “feeding”.</p>
<p>Feeding produces a disk of gas and dust that surrounds the black hole. When the material in the disk falls inward toward the black hole, friction heats the accretion disk to millions of degrees. These hot disks of matter emit a tremendous amount of X-rays. The first black hole to be detected in this manner is the famed <a href="https://doi.org/10.1038/235271b0">Cygnus X-1 system</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two images, one showing a red box in a starry sky and another showing a red disk siphoning matter from a bright white star." src="https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=250&fit=crop&dpr=1 600w, https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=250&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=250&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=315&fit=crop&dpr=1 754w, https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=315&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/475702/original/file-20220722-3516-poic2t.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=315&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On the left is an optical image showing Cygnus X-1 outlined by a red box. On the right is an artist rendition showing the outer layers of the black hole siphoning off matter from the companion star and forming an accretion disk.</span>
<span class="attribution"><a class="source" href="https://chandra.harvard.edu/photo/2011/cygx1/">X-ray: NASA/CXC; Optical: Digitized Sky Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Astronomers have known for years that <a href="https://doi.org/10.1051/0004-6361/201629844">VFTS 243 is a binary system</a>, but whether the system is a pair of stars or a dance between a single star and a black hole was unclear. To determine which was true, the team studying the binary used a technique called <a href="https://www.aanda.org/articles/aa/abs/2009/04/aa10810-08/aa10810-08.html">spectral disentangling</a>. This technique separates the light from VFTS 243 into its constituent wavelengths, which is similar to what happens when white light enters a prism and the different colors are produced. </p>
<p>This analysis revealed that the light from VFTS 243 was <a href="https://doi.org/10.1038/s41550-022-01730-y">from a single source, not two separate stars</a>. With no detectable radiation emanating from the star’s companion, the only possible conclusion was that the second body within the binary is a black hole and thus the first dormant black hole found outside of the Milky Way galaxy. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&rect=4%2C19%2C725%2C414&q=45&auto=format&w=1000&fit=clip"><img alt="A black dot and a big blue star spinning around each other." src="https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&rect=4%2C19%2C725%2C414&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/475696/original/file-20220722-16-rv47o6.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In the VFTS 243 system, the stellar companion and black hole (which are not shown to scale) orbit each other. Notice that there is no accretion disk present.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/videos/eso2210b/">ESO/L. Calçada</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Why is VFTS 243 important?</h2>
<p>Most black holes with a mass of less than 100 Suns are formed from the collapse of a massive star. When this happens, often there is a <a href="https://spaceplace.nasa.gov/supernova/en/">tremendous explosion known as a supernova</a>.</p>
<p>The fact that the black hole in VFTS 243 system is in a circular orbit with the star is strong evidence that there was no supernova explosion, which otherwise might have <a href="https://doi.org/10.1093/mnras/stz2335">kicked the black hole</a> out of the system – or at the very least disrupted the orbit. Instead, it appears that the progenitor star <a href="https://doi.org/10.3847/0004-637X/821/1/38">collapsed directly</a> to form the black hole sans explosion. </p>
<p>The massive star in the VFTS 243 system will live for only another 5 million years – a blink of an eye in astronomical timescales. The death of the star should result in the formation of another black hole, transforming the VFTS 243 system into a black hole binary.</p>
<p>To date, astronomers have detected nearly 100 events where binary black holes merge and <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">produced ripples in space-time</a>. But how these binary black hole systems form is still unknown, which is why VFTS 243 and similar yet-to-be-discovered systems are so vital to future research. Perhaps nature has a sense of humor – for black holes are the darkest objects in existence and emit no light, yet they illuminate our fundamental understanding of the universe.</p><img src="https://counter.theconversation.com/content/187419/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Idan Ginsburg does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Astronomers have discovered the first dormant black hole outside of the Milky Way. These black holes are not absorbing matter from a nearby star, making them incredibly hard to find.Idan Ginsburg, Academic Faculty in Physics & Astronomy, Georgia State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1792432022-03-28T12:37:15Z2022-03-28T12:37:15ZAstronomy’s 10-year wish list: Big money, bigger telescopes and the biggest questions in science<figure><img src="https://images.theconversation.com/files/454218/original/file-20220324-27-noyr0p.jpg?ixlib=rb-1.1.0&rect=2%2C29%2C1464%2C924&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Hubble Space Telescope was born from a previous decadal survey. What leaps forward will come from this one?</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasa2explore/9772693411/in/photolist-fTzBgZ-fV7Nk9-fQaif5-fWzu7e-fTBCFF-fV7KZh-fWHXsP-5h3tfy-6ntttp-fWznYG-fWzU9R-fWHXsZ-fTBgaC-6gJpSm-fWHBSs-6nttrR-fWzj7z-fgjn2y-fWzjfk-5hdDA9-5h9hLv-5h9hrv-fWzuwx-6cZGVe-fV84vM-6nttwi-6nxAXS-6d4RFY-fTB8nm-fWxNSU-fWy8JU-fV7KDY-6d4RAA-fWxrAA-6fXHbJ-fV7Na9-fV84oH-fTB85j-6d6CVo-fWy9Tq-fg8qA3-fWyfu7-fWxyLj-6fTwAk-fWxz2N-fV88pZ-6fXH8C-6nLgWt-6fXH2o-6nQraS">NASA Johnson/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>It takes expensive tools to learn about the universe, but projects like the <a href="https://www.vla.nrao.edu/">Very Large Array for radio astronomy</a> in New Mexico and the <a href="https://www.nasa.gov/mission_pages/chandra/main/index.html">Chandra X-ray Observatory</a>, which orbits Earth, have pushed scientific knowledge forward in ways that would not have been possible without these instruments. Every 10 years, astronomers and astrophysicists outline priorities for the hardware they need in the decadal survey on astronomy and astrophysics. The newest version of the survey was published by the National Academies of Sciences, Engineering and Medicine in late 2021, and debates about funding are in full swing for the next fiscal year.</p>
<p>I’m a professor of astronomy whose <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">research</a> has depended on facilities and equipment built after a recommendation in one of these decadal surveys, and I was involved in <a href="https://www.nap.edu/catalog/12982/panel-reports-new-worlds-new-horizons-in-astronomy-and-astrophysics">the previous survey</a>, published in 2010. </p>
<p>The<a href="https://www.nationalacademies.org/our-work/decadal-survey-on-astronomy-and-astrophysics-2020-astro2020"> most recent wish list</a> is full of fascinating projects, and it will be exciting to see which get funded and what research will come from them.</p>
<h2>A meeting of the minds</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The cover of the report showing planets and stars." src="https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=776&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=776&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=776&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=975&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=975&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454196/original/file-20220324-19-l2a6rr.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=975&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The new report sets detailed goals for the next decade and beyond for astronomy and astrophysics research.</span>
<span class="attribution"><a class="source" href="https://www.nap.edu/catalog/26141/pathways-to-discovery-in-astronomy-and-astrophysics-for-the-2020s">National Academies of Science, Engineering and Medicine</a></span>
</figcaption>
</figure>
<p>Every 10 years since the 1960s, U.S. astronomers and astrophysicists have gathered to create a priority list for new facilities and instruments.</p>
<p>The decadal survey of astronomers is influential because it forces everyone to be on the same page and make hard choices. It has to <a href="https://www.planetary.org/articles/the-2020-astrophysics-decadal-survey-guide">temper ambition with realism</a>, but when astronomers and astrophysicists from the many subfields all work together, they come up with ideas that advance the whole field.</p>
<p>The most <a href="https://www.nationalacademies.org/our-work/decadal-survey-on-astronomy-and-astrophysics-2020-astro2020">recent report</a> is titled “Pathways to Discovery in Astronomy and Astrophysics for the 2020s.” It’s directed at Congress and the three federal agencies that fund most astronomical research: NASA, the National Science Foundation and the Department of Energy. Billions of dollars are at stake.</p>
<p>Producing the reports is a massive undertaking, involving 20 people on the main committee and over 1,000 contributing to the final report. The committee reviewed <a href="https://baas.aas.org/astro2020-science">573 white papers</a> all arguing for specific projects and astronomical capabilities. The finished report runs 615 pages, and it’s not light reading.</p>
<p>This approach works. Some of NASA’s most ambitious and fruitful scientific missions – like the Hubble and James Webb space telescopes – were proposed in and funded through decadal surveys. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artists representation of an exoplanet." src="https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454215/original/file-20220324-25-750p9f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gaining better knowledge of planets outside the solar system – and searching them for signs of life – is a major goal the research community listed in the report.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Kepler186f-ArtistConcept-20140417.jpg#/media/File:Kepler186f-ArtistConcept-20140417.jpg">NASA Ames/SETI Institute/JPL-Caltech via Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>Big science</h2>
<p>The committee identified 24 key science questions for the next generation of astronomy. These fall into three major themes that are science at the biggest scale, and the facilities on the wish list are designed to address these themes.</p>
<p>First is the study of Earth-like worlds. Thanks to explosive growth in the <a href="https://exoplanets.nasa.gov/discovery/exoplanet-catalog/">discovery of exoplanets</a>, the number of known planets outside the solar system has been <a href="https://exoplanets.nasa.gov/faq/6/how-many-exoplanets-are-there/">doubling</a> roughly every two years. Among the <a href="https://exoplanets.nasa.gov/news/1702/cosmic-milestone-nasa-confirms-5000-exoplanets/">more than 5,000</a> known exoplanets are several hundred that are <a href="https://dx.doi.org/10.1073%2Fpnas.1319909110">similar to Earth</a> and could potentially support life. A major goal for the next decade is to build new large telescopes on the ground and in space with instruments that can <a href="https://doi.org/10.1073/pnas.1304213111">“sniff” the atmospheres</a> of Earth-like planets to try to detect gases like oxygen that are created by microbes.</p>
<p>Second is to advance <a href="https://astronomy.com/magazine/news/2021/06/the-age-of-multi-messenger--astronomy">multimessenger astronomy</a> – a relatively new field of astrophysics that takes information about <a href="https://theconversation.com/ligo-detects-more-gravitational-waves-from-even-more-ancient-and-distant-black-hole-collisions-78571">gravitational waves</a>, <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">elementary particles</a> and <a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">electromagnetic radiation</a> and combines it all to gain deeper insights into the underlying astrophysics of the universe. In this case, the need is not so much for new scientific tools but for more grants to enable researchers to collaborate and share data. The science goal is to learn more about cosmic explosions and mergers of compact objects like neutron stars and black holes. </p>
<p>The final theme is the study of <a href="https://blog.oup.com/2020/11/supermassive-black-holes-monsters-in-the-early-universe/">cosmic ecosystems</a>, especially the origin and evolution of galaxies and the massive black holes at their centers. By looking at extremely distant galaxies, astronomers can look into the past, since light takes time to reach Earth. So to understand these massive, complicated systems, scientists will need giant optical telescopes to find galaxies far away in the young universe, as well as radio telescopes to peer into their dusty hearts and reveal the black holes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A telescope in space next to a large shade structure." src="https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454216/original/file-20220324-21-1kjstrt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The report requested a large telescope to study exoplanets, similar to one NASA has developed that would use a shade to block light from a distant star to facilitate the study of planets around that star.</span>
<span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA20911">NASA/JPL</a></span>
</figcaption>
</figure>
<h2>Astronomy’s wish list</h2>
<p>Here are a few particularly exciting highlights from the hundreds of items on the wish list.</p>
<p>First, the report recommends spending US$1 billion on developing technology with which to build the next generation of “<a href="https://www.space.com/nasa-great-observatories-space-telescope-decadal-survey">great observatories</a>” in space. The flagship of these missions – to be launched in the 2040s with an eye-popping price tag of $11 billion – would be an <a href="https://aerospaceamerica.aiaa.org/decadal-survey-wants-nasa-to-rethink-how-it-designs-space-telescopes/">optical telescope with a massive 20-foot (6-meter) mirror</a>. This mirror would be eight times bigger than Hubble’s and would be designed to study Earth-like planets in other solar systems – and potentially detect life. The report also recommends building <a href="https://www.aip.org/fyi/2021/astro2020-decadal-survey-arrives-priorities-major-facilities">two smaller space telescopes</a> to work at infrared and X-ray wavelengths, each at a cost of $3 billion to $5 billion.</p>
<p>But orbital efforts are not the only aims of the report. The report also asks for funds to build a giant optical telescope on Earth with a diameter of 80 to 100 feet (25 to 30 meters). That’s five to seven times the light-collecting area of today’s largest telescope. <a href="https://www.science.org/content/article/rival-giant-telescopes-join-forces-seek-us-funding">Two proposals</a> are competing to build this telescope, which would cost close to $2 billion.</p>
<p>The report also calls for the National Science Foundation to spend $3 billion on a new array of <a href="https://ngvla.nrao.edu/">263 radio telescopes</a> that would span the entire U.S. This telescope array could produce radio images with 10 times the sensitivity and 20 times the sharpness of any previous facility, allowing scientists to see deeper into the universe and discover previously undetectable objects. Another item on the wish list is a $650 million pair of <a href="https://cmb-s4.org/">microwave telescopes in Chile and Antarctica</a> that would map the afterglow of the Big Bang.</p>
<p>This kind of money is needed to achieve scientific goals of this scope.</p>
<h2>State of the profession</h2>
<p>Science is more than just the pursuit of knowledge. As part of recent decadal surveys, astronomers and astrophysicists have taken the opportunity to gaze inward and judge the state of the profession. This includes looking at diversity and inclusion, workplace climates and the contributions of astronomers to education and outreach.</p>
<p>[<em>Like what you’ve read? Want more?</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-likethis">Sign up for The Conversation’s daily newsletter</a>.]</p>
<p>These fields are overwhelmingly white, with people from minority backgrounds making up <a href="https://www.aip.org/statistics/reports/beyond-representation-data-improve-situation-women-and-minorities-physics-and">only 4% of faculty and students</a>. In an appendix to the report, teams <a href="https://www.nationalacademies.org/our-work/astro2020-panel-on--stateof-the-profession-and-societal-impacts">suggested a number of remedies</a> for the lack of diversity and equity. These <a href="https://nap.edu/resource/26141/interactive/">included ideas</a> such as better mentoring to reduce the high attrition rate for minority students, along with funding for bridge programs to help minorities get established early in their careers and to treat harassment and discrimination as forms of <a href="https://doi.org/10.1038/d41586-018-05076-2">scientific misconduct</a>.</p>
<p>If even a small part of the wish list becomes reality, it will not only increase our understanding of the universe, but also – just as importantly – lead to a more diverse and compassionate astronomy and astrophysics community.</p><img src="https://counter.theconversation.com/content/179243/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>The astronomy and astrophysics decadal survey for the 2020s lays out plans to search for life on distant planets, understand the formation of galaxies and solve deep mysteries of physics.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1766022022-02-07T13:58:52Z2022-02-07T13:58:52ZAstronomers think they’ve just spotted an ‘invisible’ black hole for the first time<figure><img src="https://images.theconversation.com/files/444789/original/file-20220207-17-1opuin2.jpg?ixlib=rb-1.1.0&rect=0%2C75%2C4476%2C2510&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Concept of a black hole acting as a lens on background light.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/black-hole-gravitational-lens-effect-milky-662787748">Dotted Yeti/Shutterstock</a></span></figcaption></figure><p>Astronomers famously <a href="https://theconversation.com/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167">snapped the first</a> ever direct image of a black hole in 2019, thanks to material glowing in its presence. But many black holes are actually near impossible to detect. Now another team using the <a href="https://theconversation.com/hubbles-deep-field-images-of-the-early-universe-are-postcards-from-billions-of-years-ago-40519">Hubble Space Telescope</a> seems to have finally found something nobody has seen before: a black hole which is completely invisible. The research, which has been <a href="https://arxiv.org/abs/2201.13296">posted online</a> and submitted for publication in the Astrophysical Journal, is yet to be peer-reviewed.</p>
<p>Black holes are what’s left after large stars die and their cores collapse. They are incredibly dense, with gravity so strong that nothing can move fast enough to escape them, including light. Astronomers are <a href="https://theconversation.com/a-brief-history-of-black-holes-107298">keen to study</a> black holes because they can tell us a lot about the ways that stars die. By measuring the masses of black holes, we can learn about what was going on in stars’ final moments, when their cores were collapsing and their outer layers were being expelled.</p>
<p>It may seem that black holes are by definition invisible – they after all earned their name through their ability to trap light. But we can still detect them through the way they interact with other objects thanks to their strong gravity. Hundreds of small black holes have been detected by the way they interact with other stars. </p>
<p>There are two different approaches to such detection. In “<a href="https://www.cosmos.esa.int/web/cesar/x-ray-binaries-monitoring">X-ray binary stars</a>” – in which a star and a black hole orbit a shared centre while producing X-rays – a black hole’s gravitational field can pull material from its companion. The material circles the black hole, heating up by friction as it does so. The <a href="https://theconversation.com/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167">hot material glows</a> brightly in X-ray light, making the black hole visible, before being sucked into the black hole and disappearing. You can also detect pairs of black holes as they merge together, spiralling inwards and emitting a brief flash of <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">gravitational waves</a>, which are ripples in spacetime.</p>
<figure class="align-center ">
<img alt="Image of a black hole." src="https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/440259/original/file-20220111-16-71qdkv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">First image of a black hole.</span>
<span class="attribution"><span class="source">Event Horizon Telescope collaboration et al.</span></span>
</figcaption>
</figure>
<p>There are many rogue black holes that are drifting through space without interacting with anything, however – making them hard to detect. That’s a problem, because if we can’t detect isolated black holes, then we can’t learn about <a href="https://theconversation.com/black-holes-we-think-weve-spotted-the-mysterious-birth-of-one-174726">how they formed</a> and about the deaths of the stars they came from. </p>
<h2>New, dark horizons</h2>
<p>To discover such an invisible black hole, the team of scientists had to combine two different types of observations over several years. This impressive achievement promises a new way of finding the previously elusive class of isolated black holes.</p>
<p>Einstein’s <a href="https://theconversation.com/will-we-have-to-rewrite-einsteins-theory-of-general-relativity-50057">General Theory of Relativity</a> predicted that massive objects will bend light as it travels past them. That means that any light passing very close to an invisible black hole – but not close enough to end up inside it – will be bent in a similar way to light passing through a lens. This is called <a href="https://theconversation.com/how-we-managed-what-einstein-thought-was-impossible-and-used-his-theory-to-weigh-a-star-79050">gravitational lensing</a>, and can be spotted when a foreground object aligns with a background object, bending its light. The method has already been used to study everything from clusters of galaxies to planets around other stars. </p>
<p>The authors of this new research combined two types of gravitational lensing observations in their search for black holes. It started with them spotting light from a distant star suddenly magnify, briefly making it appear brighter before going back to normal. They could not see any foreground object that was causing the magnification via the process of gravitational lensing, though. That suggested the object might be a lone black hole, something which had never been seen before. The problem was that it could also just have been a faint star.</p>
<p>Figuring out if it was a black hole or a faint star required a lot of work, and that’s where the second type of gravitational lensing observations came in. The authors repeatedly took images with Hubble for six years, measuring how far the star appeared to move as its light was deflected. </p>
<p>Eventually this let them calculate the mass and distance of the object which caused the lensing effect. They found it was about seven times the mass of our Sun, located about 5,000 light years away, which sounds far away but is actually relatively close. A star that size and that close should be visible to us. Since we can’t see it, they concluded it must be an isolated black hole.</p>
<p>Taking that many observations with an observatory like Hubble isn’t easy. The telescope is very popular and there is a lot of competition for its time. And given the difficulty of confirming an object like this, you might think the prospects for finding more of them aren’t great. Luckily, we’re at the beginning of a revolution in astronomy. This is thanks to a new generation of facilities, including the ongoing <a href="https://sci.esa.int/web/gaia">Gaia survey</a>, and upcoming <a href="https://www.lsst.org/science">Vera Rubin Observatory</a> and <a href="https://roman.gsfc.nasa.gov/">Nancy Grace Roman Space Telescope</a>, all of which will take repeated measurements of large parts of the sky in unprecedented detail.</p>
<p>That’s going to be huge for all areas of astronomy. Having regular, high-precision measurements of so much of the sky will let us investigate en masse things which change on very short timescales. We’ll study things as varied as asteroids, exploding stars known as supernovas, and planets around other stars in new ways.</p>
<p>When it comes to the search for invisible black holes, that means rather than celebrating finding just one, we could soon be finding so many that it becomes routine. That will let us fill in the gaps in our understanding of the deaths of stars and the creation of black holes. </p>
<p>Ultimately, the galaxy’s invisible black holes are about to find it much harder to hide.</p><img src="https://counter.theconversation.com/content/176602/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam McMaster receives funding from the Science and Technology Facilities Council, DISCnet, and the Open University Space SRA.</span></em></p><p class="fine-print"><em><span>Andrew Norton has previously received funding from the UK Science & Technology Facilities Council. </span></em></p>Some black holes are isolated in space and therefore near impossible to detect.Adam McMaster, Postgraduate Research Student (PhD) in Astronomy, The Open UniversityAndrew Norton, Professor of Astrophysics Education, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1645022021-07-15T15:06:58Z2021-07-15T15:06:58ZBig bang: how we are trying to ‘listen’ to it – and the new physics it could unveil<figure><img src="https://images.theconversation.com/files/411445/original/file-20210715-32735-1ak3sbm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5000%2C2813&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What happened during the Big Bang?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/big-bang-space-birth-universe-3d-1052269634"> FlashMovie/Shutterstock</a></span></figcaption></figure><p>Exactly what happened at the beginning of the universe, 14 billion years ago, is one of the greatest mysteries in physics – there’s no simple way to probe it. That’s because, <a href="https://theconversation.com/what-would-it-have-been-like-to-witness-the-beginning-of-the-universe-90043">in its early stages</a>, the universe was filled with a dense plasma – a gas made out of charged particles including electrons and protons (particles that comprise the atomic nucleus alongside neutrons). Photons (particles of light) were trapped in the mix, bouncing off the other particles furiously, with no way to escape.</p>
<p>As the universe expanded and the density decreased enough, photons could finally escape and light started travelling freely. This event, happening 380,000 years after the big bang, dubbed “recombination”, gave rise to the first snapshot of the universe’s origin – the <a href="https://theconversation.com/the-cmb-how-an-accidental-discovery-became-the-key-to-understanding-the-universe-45126">cosmic microwave background</a> – which we observe with telescopes. Most of what we know about the early universe is based on this leftover radiation from the big bang. But recombination acts like a wall: we cannot directly probe earlier epochs with telescopes, as light was trapped at that time.</p>
<p>Now several projects are trying to listen to the big bang using gravitational waves – <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">ripples in the very fabric of spacetime</a>. Our <a href="http://www.ctc.cam.ac.uk/activities/UHF-GW.php">new project</a>, will aim to detect such waves at ultra-high frequencies, and could lead to the discovery of brand new physics.</p>
<p>The recent <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">detections of gravitational waves</a>, <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">ripples in the very fabric of spacetime</a>, by the <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">Ligo/Virgo experiments</a> have opened <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">a new window of observation</a> onto the universe. They enable us to investigate phenomena in which gravity, instead of light, is the messenger. The gravitational waves detected so far are called astrophysical gravitational waves – they are created by relatively recent physical processes, such as mergers of black holes. </p>
<p>The type of waves that might be produced in the early universe are called <a href="https://iopscience.iop.org/article/10.1088/1361-6382/aac608">cosmological gravitational waves</a> and have not yet been detected. Such waves travel freely after being produced; they act like ghosts that can go through the recombination wall and provide a unique tool to investigate the early universe. While astrophysical gravitational waves come from a precise direction in the sky, cosmological ones reach us from all possible directions, corresponding to different regions where they were produced in the past. This makes them very hard to detect.</p>
<p>But the reward of being able to detect cosmological gravitational waves would be huge: there are many possible cataclysmic phenomena in the early universe that could produce them. <a href="https://www.newscientist.com/article/mg21829224-100-cosmic-preheating-baked-planets-stars-and-people/">Preheating</a>, for instance, can be thought of as a series of explosions during which the energy was transferred from the unknown particles driving <a href="https://theconversation.com/shape-of-the-universe-could-it-be-curved-not-flat-126721">inflation</a> – an era when the universe blew up in size – to particles described in the <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">Standard Model of particle physics</a> today. This occurred when the universe was a fraction of a second old, immediately after the end of inflation. It is also very likely that the universe changed state a few times (as water does when boiled) during its first second: such events are called phase transitions.</p>
<p>Processes involving yet undiscovered particles such as <a href="https://www.scientificamerican.com/article/is-dark-matter-made-of-axions/">axions</a> (which may make up dark matter) could also have produced the waves. So if cosmological gravitational waves are detected, they could give us crucial information about what happened at the beginning of time.</p>
<h2>High versus low frequency</h2>
<p>Current and <a href="https://theconversation.com/lisa-pathfinder-will-pave-the-way-for-us-to-see-black-holes-for-the-first-time-51374">planned</a> gravitational wave detectors mostly focus on low frequencies, where astrophysical signals are guaranteed to exist. These can also look for cosmological gravitational waves and will be able to probe signals produced when the universe was extremely young, bar <a href="https://theconversation.com/shape-of-the-universe-could-it-be-curved-not-flat-126721">the very first moments</a> after inflation.</p>
<p>That’s because the wavelength of a produced wave is proportional to the “size” of the universe (that is expanding). The earlier it was produced, the smaller the corresponding wavelength – and the higher the frequency. The era immediately after the end of inflation is what we are aiming to probe with our new project. This covers times when we could see actual evidence for some of the most fascinating theories of nature, such as <a href="https://theconversation.com/stephen-hawking-had-pinned-his-hopes-on-m-theory-to-fully-explain-the-universe-heres-what-it-is-93440">string theory</a>.</p>
<p>There are also other possible sources that would produce high-frequency gravitational waves in the more recent universe. Examples include mysterious objects called boson stars (stars made out of elementary particles called bosons) or “primordial black holes”, which <a href="https://www.quantamagazine.org/black-holes-from-the-big-bang-could-be-the-dark-matter-20200923/">might compose dark matter</a>. These are both hypothetical entities thought to exist that have never been observed.</p>
<p>The vast majority of signals at high frequency would immediately point to particles or phenomena that cannot be described within the <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">Standard Model of particle physics</a> and the <a href="https://www.universetoday.com/84730/astronomy-without-a-telescope-assumptions/">Standard Model of cosmology</a>, our best descriptions of nature. So a discovery would shed light on some of the unsolved problems of our universe, such as the composition of dark matter and the origin of inflation.</p>
<h2>Tiny machinery</h2>
<p>There are a couple of clear advantages of high-frequency detectors. First, as the size of the detector is proportional to the wavelength to be probed, high-frequency gravitational wave detectors would be much smaller (and cheaper) than low-frequency ones. The length of the Ligo arms, for instance, is four kilometres. We dream of listening to the sound of the big bang with a detector that would fit in our kitchen. We are hopeful this could work – at high frequency there are no astrophysical background signals interfering with what we want to measure.</p>
<figure class="align-center ">
<img alt="Aerial view of LIGO facility in Hanford, Washington." src="https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=602&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=602&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=602&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=756&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=756&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411446/original/file-20210715-15-1o64zv8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=756&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aerial view of LIGO facility in Hanford, Washington.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/WA/image/ligo20150731a">Caltech/wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Detecting high-frequency gravitational waves is hard though. An experiment like Ligo looks for the variation of the distance between two mirrors, caused by the passing gravitational wave, equivalent to a fraction of the size of the nucleus of an atom. As high-frequency gravitational waves detectors are smaller, the variation to be detected would be even tinier. </p>
<p>With our currently available technology, we are already able to detect minute variations in the high-frequency range (though we haven’t caught any gravitational waves yet). But we need to improve it a bit more to detect gravitational waves from the early universe. Supporting this technological development is what <a href="http://www.ctc.cam.ac.uk/activities/UHF-GW.php">our project</a> is all about.</p>
<p>Ultimately, we are trying to start a challenging journey, much as people did back in the 1970s when they began searching for astrophysical gravitational waves. It took almost 50 years and more than 20 attempts, which ultimately shows that hard work and patience pay off.</p><img src="https://counter.theconversation.com/content/164502/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Francesco Muia is funded by a UKRI/EPSRC Stephen Hawking fellowship and partially supported by an STFC consolidated grant.</span></em></p>How scientists are planning to listen to the sound of the big bang with a gravitational wave detector that would fit in a kitchen.Francesco Muia, Postdoctoral Researcher, Theoretical Physics and Cosmology, Stephen Hawking Fellow, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1625262021-06-30T14:02:05Z2021-06-30T14:02:05ZWhat happens when black holes collide with the most dense stars in the universe<p>For the first time, a faint signal caused by the merging of two almost equally mysterious objects – a black hole and a neutron star – has <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac082e">been recorded on Earth</a>.</p>
<p>On January 5 2020, when the world was first learning of the COVID-19 outbreak, gravitational waves from this merging reached the Livingston detector of the <a href="https://www.ligo.caltech.edu/page/what-is-ligo">Laser Interferometer Gravitational-wave Observatory (Ligo</a>) gravitational wave observatory in Louisiana, US. </p>
<p>On January 15, the second gravitational wave event from a merger between a black hole and a neutron star, the densest stars in the universe, was discovered.</p>
<p>These two recordings are the first mergers between a black hole and a neutron star to have been detected on Earth. Black hole-neutron star binary systems, where a black hole and a neutron star orbit each other, <a href="https://www.frontiersin.org/articles/10.3389/fspas.2020.00046/full">had been predicted</a> but never observed – until now.</p>
<p><a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">Gravitational waves</a> are distortions in space-time, predicted by Albert Einstein’s general theory of relativity. </p>
<p>In a <a href="https://theconversation.com/five-myths-about-gravitational-waves-46493">gravitational wave observatory</a>, the distance between two suspended mirrors is measured with a laser. The measurement technique relies on the overlap of reflected laser light within the experiment. Two light waves are arranged so that the signals cancel each other out exactly. Changing the distance between the mirrors by even a tiny fraction of a wavelength produces a measurable light signal.</p>
<p>The basic idea behind the theory of relativity is that space itself possesses a kind of elastic structure, even in the absence of any matter. Similar to an inflated balloon, you can squeeze it one way and it expands in the perpendicular direction. </p>
<p>Relativity predicts that matter warps space (and time) and a collision between two compact objects like a black hole and a neutron star rapidly changes the compression and relaxation of the space in the vicinity of the objects. Waves of periodic compression and expansion are emitted. The way to measure these waves is to monitor the distance between two otherwise fixed objects, because the gravitational wave will periodically change the extent of the space between these objects, as it passes.</p>
<p>During the first ever detected gravitational wave event in 2015, for which three physicists were awarded <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">the Nobel prize in 2017</a>, the distances between the mirrors in the two stations of the LIGO observatory, which are 4km (2.5 miles) apart, changed by about a thousandth of a trillionth of a millimetre. </p>
<p>The merger detected in 2015 was between two comparatively massive black holes, each around 30 times the mass of the Sun. Since then, the sensitivity of the instrument has been improved. Now also a smaller, less sensitive, gravitational wave observatory in Italy, called <a href="https://www.virgo-gw.eu/">the Virgo experiment</a>, is frequently used as part of the telescope network. </p>
<p>In the new discoveries, the merging objects each had less than ten times the mass of the Sun. The event on January 5 involved objects with respective masses of 8.9 and 1.9 times the mass of the Sun, and the merger on January 15 was between objects with 5.7 and a 1.5 times the mass of the Sun.</p>
<h2>Neutron stars</h2>
<p>It’s important that the smaller masses were below 2.2 times the mass of the Sun, because this suggests these objects were neutron stars. Neutron stars are so dense that an amount of matter comparable to the solar system is compressed to a diameter of about 20km.</p>
<p>The matter in a neutron star is so dense that atoms get crushed, resulting in the formation of neutrons. The strong gravity on their surface makes them, in their own right, interesting laboratories to study effects of general relativity. </p>
<p>When a neutron star becomes even more massive, for example when some interstellar gas falls on it, the nuclear forces can no longer resist gravity and the star collapses to a black hole, an object so compact that not even light can resist its gravitational pull.</p>
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Read more:
<a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">How we discovered gravitational waves from 'neutron stars' – and why it's such a huge deal</a>
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<p>Neutron stars and black holes are not that rare in the Milky Way. They are a common outcome from the evolution of stars significantly more massive than the Sun. Such massive stars often occur in binary systems, with two stars orbiting each other.</p>
<p>It’s not surprising to find neutron stars and black holes in binary systems, where they are locked in a gravitational dance. Such binaries emit gravitational waves for their entire lifetime.</p>
<h2>Binary systems</h2>
<p>The energy for the gravitational waves comes from the motion of the objects around each other. As the system emits gravitational waves, the objects get closer together. This makes the gravitational wave emission increase and, finally, the two merge into a new, bigger black hole, with a burst of gravitational wave emission. This is what is detectable on Earth.</p>
<p>While it was expected that neutron star-black hole systems existed, we’d never been able to spot them before. Neutron stars emit radio and X-ray emissions, which can now be routinely detected. Other than looking for gravitational waves, black holes can only be observed when something falls on them – a star or interstellar gas, for example.</p>
<p>If a black hole has a normal star companion, it can capture mass from the companion which emits X-rays before it disappears into the black hole. Binary black holes have no obvious source of gas, and they’re known only from gravitational wave experiments. </p>
<p>A neutron star-black hole system could in principle be discovered with radio telescopes, but – so far – the search has not been successful. This new discovery provides important information about the astrophysics of such systems. </p>
<p>More discoveries will surely be made, which will help to improve our understanding of what is inside neutron stars and black holes – and quite possibly also provide new tests, or proofs, of the theory of relativity.</p><img src="https://counter.theconversation.com/content/162526/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Krause receives funding from the Science and Technology Facilities Council and is a fellow of the Royal Astronomical Society, member of the Astronomische Gesellschaft, the European Astronomical Society, the International Astronomical Union and the German Physical Society.</span></em></p>The aftermath of a black hole colliding with a neutron star has been recorded on Earth.Martin Krause, Senior Lecturer, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1635752021-06-29T12:07:28Z2021-06-29T12:07:28Z‘Laws of nature turned up to 11’: astronomers spot two neutron stars being swallowed by black holes<figure><img src="https://images.theconversation.com/files/408783/original/file-20210629-19-11qb29b.jpg?ixlib=rb-1.1.0&rect=1%2C9%2C1304%2C912&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Carl Knox/OzGrav/Swinburne Univ.</span></span></figcaption></figure><p>One of the best things about being an astronomer is being able to discover something new about the universe. In fact, maybe the only thing better is discovering it twice. And that’s exactly what my colleagues and I have done, by making two separate observations, just ten days apart, of an entirely new type of astronomical phenomenon: a neutron star circling a black hole before being gobbled up.</p>
<p>The two observations were made in January 2020, by the <a href="https://www.ligo.caltech.edu/page/what-is-ligo">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> and the <a href="https://www.virgo-gw.eu/">Virgo Observatory</a>, both of which detect gravitational waves from the distant cosmos. </p>
<p>After 18 months of painstaking analysis, our discoveries are <a href="https://doi.org/10.3847/2041-8213/ac082e">published today in The Astrophysics Journal Letters</a>. The new observations open up new avenues to study the life cycle of stars, the nature of space-time, and the behaviour of matter at extreme pressures and densities.</p>
<p>The first observation of a neutron star-black hole system was made on January 5 2020. LIGO and Virgo observed gravitational waves — distortions in the very fabric of space-time — produced by the final 30 seconds of the dying orbit of the neutron star and black hole, followed by their inevitable collision. The discovery is named GW200105. </p>
<p>Remarkably, just ten days later, LIGO and Virgo detected gravitational waves from a second collision between a neutron star and a black hole. This event is named GW200115. Both collisions happened around 900 million years ago, long before the first dinosaurs appeared on Earth.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/dACjwnMhUJg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Artist’s impression of a neutron star orbiting and colliding with a black hole – Carl Knox/OzGrav/Swinburne Univ.</span></figcaption>
</figure>
<p>Neutron stars and black holes are among the most extreme objects in the universe. They are the fossil relics of massive dead stars. When a star that is more than eight times as massive as the Sun runs out of fuel, it undergoes a spectacular explosion called a supernova. What remains can be a neutron star or a black hole. </p>
<p>Neutron stars are typically between 1.5 and 2 times as massive as the Sun, but are so dense that all their mass is packed into an object the size of a city. At this density, atoms can no longer sustain their structure, and dissolve into a stream of free quarks and gluons: the building blocks of protons and neutrons.</p>
<p>Black holes are even more extreme. There is no upper limit to how massive a black hole can be, but all black holes have two things in common: a point of no return at their surface called an “event horizon”, from which not even light can escape; and a point at their centre called a “singularity”, at which the laws of physics as we understand them break down. </p>
<p>It is fair to say black holes are an enigma. One of the holy grails of 21st-century physics and astronomy is to find a deeper understanding of the laws of nature by observing these strange and extreme objects.</p>
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Read more:
<a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a>
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<h2>A new type of star system</h2>
<p>Neutron stars orbiting black hole companions have long been thought to exist. LIGO and Virgo had been searching for them for more than a decade, but they have remained elusive until now.</p>
<p>So why are we so confident we’ve now seen not one such system, but two? </p>
<p>When LIGO and Virgo observe gravitational waves, the first question on our minds is “what caused them?” To find that out, we use two things: our observational data, and supercomputer simulations of different types of astronomical events that could plausibly explain those data. </p>
<p>By comparing the simulations to our real observations, we look for those characteristics that best match our data, homing in on the likely ones and ruling out the unlikely ones.</p>
<p>For the first discovery (GW200105), we determined that the most likely source of the gravitational waves was the final few orbits, and eventual collision, between an object around 8.9 times the mass of the Sun, with an object around 1.9 times the mass of the Sun. Given the masses involved, the most plausible explanation is that the heavier object is a black hole, and the lighter one is a neutron star. </p>
<p>Similarly, from the second (GW200115), we determined that its most likely source was the final few orbits and collision of a 5.7-solar-mass black hole with a 1.5-solar-mass neutron star.</p>
<p>There is no definitive smoking gun that the lighter objects are neutron stars, and in principle they could be very light black holes, although we consider this explanation unlikely. By far the best hypothesis is that our new observations are consistent with the merger of neutron stars and black holes.</p>
<h2>Stellar fossil-hunting</h2>
<p>Our discoveries have several intriguing implications. Neutron star-black hole systems allow us to piece together the evolutionary history of stars. Gravitational-wave astronomers are like stellar fossil-hunters, using the relics of exploded stars to understand how massive stars form, live and die. </p>
<p>We have been doing this for several years with LIGO/Virgo’s observations of <a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">pairs of black holes</a> and <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">pairs of neutron stars</a>. The newly discovered rarer pairs, containing one of each, are fascinating pieces of the stellar fossil record. </p>
<p>For the first time we have directly measured the rate at which neutron stars merge with black holes: we think there are likely to be tens or hundreds of thousands such collisions across the universe per year. With more observations, we will measure the rate more precisely.</p>
<p>What happens to the neutron stars after they’ve been gobbled up? Now we’re really looking at the laws of nature turned up to 11. When neutron stars merge with black holes, they are deformed, imprinting information about their exotic form of matter onto the gravitational waves we observe on Earth. </p>
<p>This can reveal the composition of neutron stars, which in turn tells us about how quarks and gluons behave at extreme pressure and density. It doesn’t tell us what’s going on behind the black hole’s event horizon, although another aspect of our discoveries is that we can look for hints of new physics in black holes in the gravitational-wave signals.</p>
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Read more:
<a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">When black holes meet: inside the cataclysms that cause gravitational waves</a>
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<p>When LIGO and Virgo resume observing in mid-2022 after an upgrade to boost their sensitivity still further, we will see more collisions between neutron stars and black holes. In the coming decade we expect to amass thousands more gravitational-wave detections. </p>
<p>Over time we hope to piece together the laws of nature that will help us understand the inner workings of the most extreme and impenetrable objects in the universe.</p><img src="https://counter.theconversation.com/content/163575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rory Smith does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Gravitational waves reveal the demise of super-dense neutron stars spiralling into their black hole companions - the first time such strange and exotic star systems have ever been observed.Rory Smith, Lecturer in Astrophysics, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1627852021-06-17T20:05:52Z2021-06-17T20:05:52ZApproaching zero: super-chilled mirrors edge towards the borders of gravity and quantum physics<figure><img src="https://images.theconversation.com/files/406468/original/file-20210615-3629-ntfm3c.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2746%2C1835&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The <a href="https://www.ligo.caltech.edu">LIGO gravitational wave observatory</a> in the United States is so sensitive to vibrations it can detect the tiny ripples in space-time called gravitational waves. These waves are caused by colliding black holes and other stellar cataclysms in distant galaxies, and they cause movements in the observatory much smaller than a proton. </p>
<p>Now we have used this sensitivity to effectively chill a 10-kilogram mass down to less than one billionth of a degree above absolute zero.</p>
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Read more:
<a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">Explainer: why you can hear gravitational waves when things collide in the universe</a>
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<p>Temperature is a measure of how much, and how fast, the atoms and molecules that surround us (and that we are made of) are moving. When objects cool down, their molecules move less. </p>
<p>“Absolute zero” is the point where atoms and molecules stop moving entirely. However, quantum mechanics says the complete absence of motion is not really possible (due to the <a href="https://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">uncertainty principle</a>). </p>
<p>Instead, in quantum mechanics the temperature of absolute zero corresponds to a “motional ground state”, which is the theoretical minimum amount of movement an object can have. The 10-kilogram mass in our experiment is about 10 trillion times heavier than the previous heaviest mass cooled to this kind of temperature, and it was cooled to nearly its motional ground state.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Danny Sellers / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The work, <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abh2634">published today in Science</a>, is an important step in the ongoing quest to understand the gap between quantum mechanics — the strange science that rules the universe at very small scales — and the macroscopic world we see around us. </p>
<p>Plans are already under way to improve the experiment in more sensitive gravitational wave observatories of the future. The results may offer insight into the inconsistency between quantum mechanics and the theory of general relativity, which describes gravity and the behaviour of the universe at very large scales.</p>
<h2>How it works</h2>
<p>LIGO detects gravitational waves using lasers fired down long tunnels and bounced between two pairs of 40-kilogram mirrors, then combined to produce an interference pattern. Tiny changes in the distance between the mirrors show up as fluctuations in the laser intensity.</p>
<p>The motion of the four mirrors is controlled very precisely, to isolate them from any surrounding vibrations and even to compensate for the impact of the laser light bouncing off them. </p>
<p>This part may be hard to get your head around, but we can show mathematically that the <em>differences</em> in the motion of the four 40-kilogram mirrors is equivalent to the motion of a single 10-kilogram mirror. What this means is that the pattern of laser intensity changes we observe in this experiment is the same as what we would see from a single 10-kilogram mirror.</p>
<figure class="align-center zoomable">
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<figcaption>
<span class="caption">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Matt Heintze / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
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<p>Although the temperature of the 10-kilogram mirror is defined by the motion of the atoms and molecules that make it up, we don’t measure the motion of the individual molecules. Instead, and largely because it’s how we measure gravitational waves, we measure the average motion of all the atoms (or the centre-of-mass motion). </p>
<p>There are at least as many ways the atoms can move as there are atoms, but we only measure one of those ways, and that particular dance move of all the atoms together is the only one we cooled. </p>
<p>The result is that while the four physical mirrors remain at room temperature and would be warm to the touch (if we let anyone touch them), the average motion of the 10-kilogram system is effectively at 0.77 nanokelvin, or less than one billionth of a degree above absolute zero.</p>
<h2>Squeezed light</h2>
<p>Our contribution to Advanced LIGO, as members of Australia’s <a href="https://www.ozgrav.org">OzGrav</a> gravitational wave research centre, was to design, install and test the “quantum squeezed light” system in the detector. This system creates and injects a specially engineered quantum field into the detector, making it more sensitive to the motion of the mirrors, and thus more sensitive to gravitational waves.</p>
<p>The squeezed light system uses a special kind of crystal to produce pairs of highly correlated or “entangled” photons, which reduce the amount of noise in the system. </p>
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<figcaption>
<span class="caption">Australian National University scientists Nutsinee Kijbunchoo and Terry McRae build components for a quantum squeezed light source at LIGO Hanford Observatory in Washington, US.</span>
<span class="attribution"><span class="source">Nutsinee Kijbunchoo</span>, <span class="license">Author provided</span></span>
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Read more:
<a href="https://theconversation.com/were-going-to-get-a-better-detector-time-for-upgrades-in-the-search-for-gravitational-waves-100382">We're going to get a better detector: time for upgrades in the search for gravitational waves</a>
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<h2>What does it all mean?</h2>
<p>Being able to observe one particular property of these mirrors approach a quantum ground state is a by-product of improving LIGO in the quest to do more and better gravitational wave astronomy, but it might also offer insights into the vexed question of quantum mechanics and gravity. </p>
<p>At very small scales, quantum mechanics allows many strange phenomena, such as objects being both waves and particles, or seemingly existing in two places at the same time. However, even though the macroscopic world we see is built from tiny objects that must obey quantum phenomena, we don’t see these quantum effects at larger scales. </p>
<p>One theory about why this happens is the idea of <em>decoherence</em>. This suggests that heat and vibrations from a quantum system’s surroundings disrupt its quantum state and make it behave like a familiar solid object.</p>
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<img alt="" src="https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Danny Sellers / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In order to measure gravitational waves, LIGO is designed to not be affected by heat or vibrations from its surroundings, but LIGO test masses are heavy enough for gravity to be a possible cause of decoherence. </p>
<p>Despite a century of searching, we have no way to reconcile gravity and quantum mechanics. Experiments like this, especially if they can get even closer to the ground state, might yield insight into this puzzle. </p>
<p>As we improve LIGO over the next few years, we can re-do this quantum mechanics experiment and maybe see what happens when we cross over from the classical world into the quantum world with human-sized objects.</p>
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<strong>
Read more:
<a href="https://theconversation.com/explainer-gravity-5256">Explainer: gravity</a>
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<img src="https://counter.theconversation.com/content/162785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Ernest McClelland receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Robert Ward has received funding from the Australian Research Council</span></em></p><p class="fine-print"><em><span>Terry McRae receives funding from the Australian Research Council. </span></em></p>The world’s biggest gravitational wave observatory is now probing the limits of quantum mechanics.David Ernest McClelland, Distinguised Professor and Director Centre for Gravitational Astrophysics, Australian National UniversityRobert Ward, Associate Investigator, OzGrav (ARC Centre of Excellence for Gravitational Wave Discovery), Research Fellow in Physics, Australian National UniversityTerry McRae, Research fellow, gravitational wave detection, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1551252021-02-15T18:51:20Z2021-02-15T18:51:20ZA tiny crystal device could boost gravitational wave detectors to reveal the birth cries of black holes<figure><img src="https://images.theconversation.com/files/384196/original/file-20210215-15-u84vo1.jpg?ixlib=rb-1.1.0&rect=8%2C13%2C2986%2C2645&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NSF / LIGO / Sonoma State University / A Simonnet</span>, <span class="license">Author provided</span></span></figcaption></figure><p>In 2017, astronomers witnessed the birth of a black hole for the first time. Gravitational wave detectors picked up the ripples in spacetime caused by <a href="https://en.wikipedia.org/wiki/GW170817">two neutron stars colliding</a> to form the black hole, and other telescopes then observed the resulting explosion.</p>
<p>But the real nitty-gritty of how the black hole formed, the movements of matter in the instants before it was sealed away inside the black hole’s event horizon, went unobserved. That’s because the gravitational waves thrown off in these final moments had such a high frequency that our current detectors can’t pick them up.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
</strong>
</em>
</p>
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<p>If you could observe ordinary matter as it turns into a black hole, you would be seeing something similar to the Big Bang played backwards. The scientists who design gravitational wave detectors have been hard at work to figure out how improve our detectors to make it possible.</p>
<p>Today our team is publishing <a href="https://www.nature.com/articles/s42005-021-00526-2">a paper</a> that shows how this can be done. Our proposal could make detectors 40 times more sensitive to the high frequencies we need, allowing astronomers to listen to matter as it forms a black hole.</p>
<p>It involves creating weird new packets of energy (or “quanta”) that are a mix of two types of quantum vibrations. Devices based on this technology could be added to existing gravitational wave detectors to gain the extra sensitivity needed.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=464&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artist’s conception of photons interacting with a millimetre scale phononic crystal device placed in the output stage of a gravitational wave detector.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Quantum problems</h2>
<p>Gravitational wave detectors such as the <a href="https://en.wikipedia.org/wiki/LIGO">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> in the United States use lasers to measure incredibly small changes in the distance between two mirrors. Because they measure changes 1,000 times smaller than the size of a single proton, the effects of quantum mechanics – the physics of individual particles or quanta of energy – play an important role in the way these detectors work.</p>
<p>Two different kinds of quantum packets of energy are involved, both predicted by Albert Einstein. In 1905 he predicted that light comes in packets of energy that we call <em>photons</em>; two years later, he predicted that heat and sound energy come in packets of energy called <em>phonons</em>. </p>
<p>Photons are used widely in modern technology, but phonons are much trickier to harness. Individual phonons are usually swamped by vast numbers of random phonons that are the heat of their surroundings. In gravitational wave detectors, phonons bounce around inside the detector’s mirrors, degrading their sensitivity.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/australias-part-in-the-global-effort-to-discover-gravitational-waves-54525">Australia's part in the global effort to discover gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>Five years ago physicists realised you could <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.211104">solve the problem</a> of insufficient sensitivity at high frequency with devices that <em>combine</em> phonons with photons. They showed that devices in which energy is carried in quantum packets that share the properties of both phonons and photons can have quite remarkable properties. </p>
<p>These devices would involve a radical change to a familiar concept called “resonant amplification”. Resonant amplification is what you do when you push a playground swing: if you push at the right time, all your small pushes create big swinging.</p>
<p>The new device, called a “white light cavity”, would amplify all frequencies equally. This is like a swing that you could push any old time and still end up with big results.</p>
<p>However, nobody has yet worked out how to make one of these devices, because the phonons inside it would be overwhelmed by random vibrations caused by heat.</p>
<h2>Quantum solutions</h2>
<p>In <a href="https://www.nature.com/articles/s42005-021-00526-2">our paper</a>, published in Communications Physics, we show how two different projects currently under way could do the job.</p>
<p>The Niels Bohr Institute in Copenhagen has been <a href="https://www.nature.com/articles/nnano.2017.101">developing devices</a> called phononic crystals, in which thermal vibrations are controlled by a crystal-like structure cut into a thin membrane. The Australian Centre of Excellence for Engineered Quantum Systems has also demonstrated <a href="https://www.nature.com/articles/srep02132">an alternative system</a> in which phonons are trapped inside an ultrapure quartz lens.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of a tiny device that could boost gravitational wave detector sensitivity in high frequencies.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We show both of these systems satisfy the requirements for creating the “negative dispersion” – which spreads light frequencies in a reverse rainbow pattern – needed for white light cavities. </p>
<p>Both systems, when added to the back end of existing gravitational wave detectors, would improve the sensitivity at frequencies of a few kilohertz by the 40 times or more needed for listening to the birth of a black hole.</p>
<h2>What’s next?</h2>
<p>Our research does not represent an instant solution to improving gravitational wave detectors. There are enormous experimental challenges in making such devices into practical tools. But it does offer a route to the 40-fold improvement of gravitational wave detectors needed for observing black hole births.</p>
<p>Astrophysicists have predicted <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.043005">complex gravitational waveforms</a> created by the convulsions of neutron stars as they form black holes. These gravitational waves could allow us to listen in to the nuclear physics of a collapsing neutron star. </p>
<p>For example, it has been shown that they can clearly reveal whether the neutrons in the star remain as neutrons or whether they <a href="https://en.wikipedia.org/wiki/Quark_star">break up into a sea of quarks</a>, the tiniest subatomic particles of all. If we could observe neutrons turning into quarks and then disappearing into the black hole singularity, it would be the exact reverse of the Big Bang where out of the singularity, the particles emerged which went on to create our universe.</p><img src="https://counter.theconversation.com/content/155125/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. </span></em></p>A small add-on to existing gravitational wave detectors could reveal what happens to matter as it becomes a black hole, a process like the big bang in reverse.David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1454742020-09-02T14:11:17Z2020-09-02T14:11:17ZGravitational waves: astronomers spot a black hole so massive they weren’t sure it could exist<figure><img src="https://images.theconversation.com/files/356082/original/file-20200902-24-b5p3wk.jpg?ixlib=rb-1.1.0&rect=112%2C48%2C1805%2C1028&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of merging black holes.</span> <span class="attribution"><span class="source">Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)</span></span></figcaption></figure><p>One of the greatest things about being an astrophysicist is that you keep discovering things you didn’t think were possible. Now the <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> and Virgo Observatory have discovered their largest black hole yet. It’s important because scientists had in fact doubted whether black holes of this mass could even exist.</p>
<p>After months of painstaking analysis, the team has just reported their discovery in papers in the <a href="https://doi.org/10.1103/PhysRevLett.125.101102">Physical Review Letters</a> and the <a href="https://doi.org/10.3847/2041-8213/aba493">Astrophysical Journal Letters</a>.</p>
<p>The black hole was discovered because its merger with a slightly less massive companion emitted gravitational waves. These are <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">ripples in spacetime</a> that can be detected on Earth – the echoes of violent cosmic collisions that, in this case, happened billions of years ago. </p>
<p>The finding is hugely important from a research perspective. It also settles a bet among astrophysicists. In February 2017, a number of us met at the <a href="https://www.aspenphys.org/">Aspen Center for Physics</a> in Colorado, USA. We were excited to be discussing the results <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">that we already had from LIGO</a>. But we were also looking forward to future discoveries and arguing about how pairs of black holes actually merge.</p>
<p>There were multiple ideas under discussion. One was that pairs of massive stars gradually evolve side by side until both collapse into black holes and ultimately merge. Another was that previously unacquainted black holes can be brought together by the jostling of a crowd of other stars in dense stellar regions. But which is the main process? I got several participants together to make a wager, as shown on the photo below. </p>
<figure class="align-center ">
<img alt="Image of the astrophysicists signing the wager." src="https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sourav Chatterjee (now at Tata.
Institute of Fundamental Research, India); Carl Rodriguez (Carnegie
Mellon University, USA); me; Daniel Holz (University of Chicago, USA); Chris Belczynski (Nicolaus Copernicus Astronomical Center, Poland).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Violent stellar deaths</h2>
<p>At the end of their lives – when stars run out of nuclear fuel and no longer have the support pressure to counter their own gravity – they collapse. Low-mass stars, including our Sun, eventually become faint stellar ghosts <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html#:%7E:text=A%20white%20dwarf%20is%20what,core%20of%20the%20star%20remains">known as “white dwarfs”</a>. Stars that started out heavier than about eight times the mass of the Sun become incredibly dense and small objects <a href="https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html">called neutron stars</a>. And really massive stars of more than 20 solar masses at birth become black holes, with final masses between a few and around 40 solar masses. </p>
<p>But something weird has long been conjectured to happen to very, very massive stars, perhaps those with initial masses between around 130 and 250 solar masses, whose centres get really hot (around a billion degrees Kelvin) late in their evolution. The light bouncing around inside these stars, and providing much of the pressure support, is so energetic that it can transform into pairs of electrons and positrons (positrons are the antimatter counterparts of electron - they are nearly identical but have opposite charge). </p>
<p>This, in turn, makes the star unstable: the pressure suddenly drops, the centre of the star contracts and heats up, and runaway nuclear fusion causes the entire star to explode in a bright <a href="https://www.quantamagazine.org/long-lived-stellar-blast-kindles-hope-of-a-pair-instability-supernova-20190912/">“pair-instability” supernova</a>, leaving no remnant behind. </p>
<p>This means that, if all black holes in merging pairs were created by collapsing stars, there should be no black holes with masses between around 55 and 130 solar masses – the stars that could have produced such remnants would have ended their lives in explosions that leave nothing behind. More massive black holes, however, can be formed from even heavier stars (of more than 250 solar masses) which do not undergo the same runaway nuclear fusion, and collapse completely into black holes. </p>
<p>But this wouldn’t be the case for black holes merging in a crowd. When two black holes merge, they create another black hole, almost as heavy as the sum of their masses. If this black hole remains in the dense environment it can merge again, giving rise to even more massive black holes of a range of sizes, filling in the mass gap. This is what brought us to signing this bet in Aspen: would we find a merging black hole with mass between around 55 and 130 solar masses or not?</p>
<h2>Filling the (mass) gap</h2>
<p>GW190521 is a merger of two very massive black holes indeed, the heaviest of any observed so far through gravitational waves. The heavier one, measured to be between 71 and 106 solar masses (at 90% confidence), falls squarely into the mass gap. This seems to suggest that black holes do indeed repeatedly merge.</p>
<figure class="align-center ">
<img alt="Artist impression of merging black holes." src="https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The merged hole had a final mass of 142 times that of the sun, making it the largest of its kind observed in gravitational waves to date.</span>
<span class="attribution"><span class="source">LIGO/Caltech/MIT/R. Hurt (IPAC).</span></span>
</figcaption>
</figure>
<p>I was not involved in this marvellous measurement. But by a
fortuitous coincidence I had the opportunity to referee one of the discovery papers, meaning that I am now well-prepared to perform my duties as arbiter of the bet. My first order of business is to adjudicate the wager in favour of Chatterjee and Rodriguez as well as Fred Rasio of Northwestern University, US, who joined the ultimate winners in an addendum after the original bet was signed.</p>
<figure class="align-right ">
<img alt="Picture of the wager text." src="https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=731&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=731&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=731&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=919&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=919&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=919&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The bet.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Congratulations to the deserved winners – and may they enjoy the wine
owed to them, and the pleasure of being proved right. The bet being resolved, my next to-do item, along with many other astrophysicists around the world, is to start thinking about the implications of this revolutionary observation. </p>
<p>Is this the definitive demonstration of black holes merging repeatedly in a dense cluster of stars? Could we have incorrectly estimated the boundaries of the mass gap because of uncertainty in key nuclear reactions? Could the merger have happened in completely different ways we haven’t even thought of?</p>
<p>The LIGO-Virgo teams have yet again done an amazing job with their
instruments and data analysis, obtaining a wonderfully unexpected result.
For the rest of the astrophysics community, the fun of making sense of it is only just beginning. Which is why, in such scientific bets, everybody really is a winner.</p><img src="https://counter.theconversation.com/content/145474/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ilya Mandel receives funding from the Australian Research Council. </span></em></p>New discovery settles a wager between astrophysicists: black holes can merge repeatedly.Ilya Mandel, Honorary Professor of Theoretical Astrophysics, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1291382020-01-20T02:48:08Z2020-01-20T02:48:08ZA brain transplant for one of Australia’s top telescopes<figure><img src="https://images.theconversation.com/files/310788/original/file-20200120-118315-ap6mf6.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2465%2C1923&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The 22-metre radio dishes of the ATCA telescope are 30 years old but still work just fine.</span> <span class="attribution"><span class="source">John Masterson</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>One of Australia’s top telescopes will receive an A$2.6 million upgrade to help extend its three-decade record of improving our understanding of the Universe.</p>
<p>The Australia Telescope Compact Array (ATCA), near Narrabri in NSW, has been one of the top few radio telescopes in the world since it began operations in September 1988.</p>
<p>Conceived and run by CSIRO, Australia’s national science agency, ATCA ushered in a new era of astronomical discovery in this country. The construction of the telescope was nearly all Australian, triggering the development of Australian communications companies and playing a key role in the invention of fast WiFi. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=463&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=463&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=463&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=582&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=582&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310793/original/file-20200120-118311-1iezqpu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=582&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Prime Minister Bob Hawke and other VIPs at the opening of ATCA in 1988.</span>
<span class="attribution"><span class="source">John Masterson / CSIRO</span></span>
</figcaption>
</figure>
<h2>Fundamental discoveries</h2>
<p>Since that opening, thousands of astronomers from around the world have used the telescope to make fundamental discoveries about the evolution of stars and galaxies. Even now, about 450 researchers and students use it each year to study the molecules in our galaxy, the magnetic fields that thread through galaxies, and the black holes that lie at their centres. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1190&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1190&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1190&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309614/original/file-20200113-103979-3cur0i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1496&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Particles emitting radio waves (shown in purple) stream millions of lightyears into space from the supermassive black hole at the heart of the galaxy Centaurus A, as observed with the ATCA by Ilana Feain and colleagues.</span>
<span class="attribution"><span class="source">Author provided.</span></span>
</figcaption>
</figure>
<p>The ATCA has been <a href="https://sydney.edu.au/news-opinion/news/2017/10/17/gravitational-waves-world-first-discovery-down-under.html">instrumental</a> in identifying the sources of <a href="https://www.ligo.caltech.edu/page/what-is-ligo">gravitational wave signals</a>, such as colliding black holes or neutron stars. It has mapped the gas in nearby galaxies and has, unexpectedly, discovered gas in clusters of galaxies billions of light years away.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=719&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=719&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=719&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=903&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=903&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309612/original/file-20200113-103987-p6ahyg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=903&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Hydrogen gas in the Large Magellanic Cloud, a companion galaxy to our own Milky Way, observed with the ATCA by Sungeun Kim and colleagues.</span>
<span class="attribution"><span class="source">csiro</span></span>
</figcaption>
</figure>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309613/original/file-20200113-103954-jb2jkg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Carbon monoxide gas (shown in blue) in the Spiderweb cluster of galaxies, 10 billion light years away, observed with the ATCA by Bjorn Emonts and colleagues.</span>
<span class="attribution"><span class="source">M. Kornmesser / ESO.</span></span>
</figcaption>
</figure>
<h2>New telescopes</h2>
<p>Meanwhile, in the north of Western Australia, CSIRO has just completed construction of the revolutionary A$188 million Australian Square Kilometre Array Pathfinder telescope (ASKAP). </p>
<p>ASKAP is set to survey radio-frequency signals across the whole sky, increasing our knowledge of the radio sky by a factor of about 30, and providing new views of the Universe, potentially leading to <a href="https://theconversation.com/expect-the-unexpected-from-the-big-data-boom-in-radio-astronomy-84059">unexpected discoveries.</a> </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/expect-the-unexpected-from-the-big-data-boom-in-radio-astronomy-84059">Expect the unexpected from the big-data boom in radio astronomy</a>
</strong>
</em>
</p>
<hr>
<p>So you might think the 30-year old ATCA could now be retired. However, the demand for the ATCA will increase, not decrease. </p>
<p>ASKAP looks at a huge area but doesn’t see in great detail. But when ASKAP makes a new discovery, ATCA can look at it with higher resolution and using a different range of frequencies. This versatility will be vital for understanding what ASKAP’s discoveries mean.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309623/original/file-20200113-103966-4v95mz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ASKAP telescope near Murchison in Western Australia.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<h2>A new brain</h2>
<p>How do you refurbish a 30-year old telescope for a reasonable cost? The answer lies in the fact that the large dishes are only the first stage of a signal processing system, and the ATCA’s dishes are still amongst the best available. </p>
<p>Just as important as the dishes are the computing hardware and software to interpret the signals received by the dishes – these are the brain of a modern telescope. Modern computing techniques mean that this brain can be doubled in speed and versatility for a modest cost.</p>
<p>ATCA will receive A$530,000 from the <a href="https://www.arc.gov.au/news-publications/media/media-releases/investing-research-infrastructure-delivers-outcomes">Australian Research Council</a> towards an A$2.6 million project, led by Western Sydney University and CSIRO, to replace the electronic “brain” of the telescope, which was originally built using custom chips and hand-crafted code. The rest of the funding will be provided by CSIRO and other university partners.</p>
<p>AAn</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-radio-astronomy-7420">Explainer: radio astronomy</a>
</strong>
</em>
</p>
<hr>
<p>The upgraded telescope will have a state-of-art heart using <a href="https://en.wikipedia.org/wiki/Graphics_processing_unit">Graphics Processor Units</a> first designed for Playstations and Xboxes, together with modern signal processing techniques and cutting-edge software. </p>
<p>This will double the amount of bandwidth that can be observed, and make ATCA far more versatile than its old hard-wired hand-crafted brain could manage. The upgrade will vastly increase its ability to understand the science from the discoveries made with ASKAP, and to detect radio signals from gravitational wave events. </p>
<p>For example, using ASKAP we have recently discovered many strange and unexpected objects such as the two “dancing ghosts” show below.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=512&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=512&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=512&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=643&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=643&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309672/original/file-20200113-103987-1weyi7a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=643&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Two ‘dancing ghosts’ recently discovered using ASKAP, which might be a binary system of black holes about to merge.</span>
<span class="attribution"><span class="source">Baerbel Koribalski / CSIRO</span></span>
</figcaption>
</figure>
<p>The upgraded ATCA will be able to give us a detailed picture of these objects at many different frequencies, helping to locate their parent black holes and clear up what’s happening. </p>
<p>After the brain transplant, the rejuvenated ATCA will begin its second career. It will enable Australian researchers to do more ambitious research despite the increasing radio-frequency interference from radio transmitters, make more discoveries, and perhaps understand some more of the mysteries of the Universe.</p><img src="https://counter.theconversation.com/content/129138/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ray Norris receives funding from the Australian Research Council for the ATCA upgrade project described in this article. He is affiliated with CSIRO as well as Western Sydney University.. </span></em></p>An upgrade for the Australia Telescope Compact Array will enable major new discoveries about the universeRay Norris, Professor, School of Science, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1162672019-05-03T05:53:05Z2019-05-03T05:53:05ZWe’ve detected new gravitational waves, we just don’t know where they come from (yet)<figure><img src="https://images.theconversation.com/files/272121/original/file-20190501-117601-6mspoo.jpg?ixlib=rb-1.1.0&rect=425%2C189%2C3144%2C1782&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of a binary neutron star merger.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">NASA's Goddard Space Flight Center/CI Lab</a></span></figcaption></figure><p>The hunt for <a href="https://theconversation.com/au/topics/gravitational-waves-9473">gravitational waves</a> is back on with the <a href="https://www.ligo.caltech.edu/news/ligo20190502">announcement overnight</a> of the detection of signals from what’s thought to be the merger of two <a href="http://astronomy.swin.edu.au/cosmos/N/Neutron+Star">neutron stars</a>, the incredibly dense remains of a collapsed star.</p>
<p>The signals were actually picked up on Thursday April 25 — ANZAC Day here in Australia — from a binary merger named <a href="https://gracedb.ligo.org/superevents/S190425z/view/">S190425z</a>), only the second ever neutron star merger to be observed. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1121351752626909184"}"></div></p>
<p>The twin detectors of the Laser Interferometer Gravitational-Wave Observatory (<a href="https://www.ligo.caltech.edu/page/ligo-detectors">LIGO</a>) — in Washington and Louisiana in the United States — along with Virgo, located at the European Gravitational Observatory (<a href="http://www.ego-gw.it/public/virgo/virgo.aspx">EGO</a>) in Italy, only resumed their operations on April 1 after a year and a half of upgrades. The latest result shows the hunt is back with a bang. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away</a>
</strong>
</em>
</p>
<hr>
<p>This is the third observing run (named O3) and soon after the merger signal was detected, astronomers around the world started searching for a host galaxy, but this time there was an extra challenge.</p>
<h2>Where is the signal coming from?</h2>
<p>When LIGO detects <a href="http://astronomy.swin.edu.au/cosmos/G/Gravitational+Waves">gravitational waves</a> — the ripples in space-time predicted by Albert Einstein — we can work out some information quite accurately, such as the mass of merging neutron stars.</p>
<p>The images (below) of all the signals detected in the first and second observing runs of the detectors (named O1 and O2) show how each signal is unique. These differences allow us to work out the masses and distances to the objects.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=430&fit=crop&dpr=1 754w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=430&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=430&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gravitational wave events detected by LIGO before O3. Each signal is different, revealing the properties of the merging objects.</span>
<span class="attribution"><a class="source" href="https://www.ligo.org/detections/O1O2catalog.php">LIGO/VIrgo/Georgia Tech/S. Ghonge & K. Jani</a></span>
</figcaption>
</figure>
<p>But one thing that is harder to work out is <em>where</em> the signal is coming from?</p>
<p>We do this by triangulating the signal received at the three detectors (the two LIGO detectors in the US and the Virgo detector in Italy).</p>
<p>For the first detection of merging binary neutron stars, <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161101" title="GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral">GW170817</a>, we got lucky. We were able to narrow down the signal to a region of 28 square degrees on the sky (about 140 times the area of the full Moon).</p>
<p>But S190425z was only detected in a single LIGO detector and Virgo, and hence the localisation region was 10,000 square degrees. That’s about a quarter of the entire sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">LIGO localisation for the neutron star merger S190425z. The area covers about a quarter of the entire sky.</span>
<span class="attribution"><span class="source">LIGO</span></span>
</figcaption>
</figure>
<p>The neutron star merger is also estimated to have happened about 500 million light-years away from Earth. </p>
<h2>Needle in a haystack</h2>
<p>Astronomers around the world, including Australian teams, have been using telescopes from the outback of Western Australia to The Canary Islands in the Atlantic Ocean, to search for possible counterparts: galaxies that could be hosting the neutron star merger.</p>
<p>To do this we had to work out which of the 45,000 possible galaxies in the region would be the most likely hosts.</p>
<p>No confirmed matches have been found, so far, but on the way, we’ve found lots of other interesting events such as new supernovae - the explosions that occur when massive stars die.</p>
<p>This effort is an integral part of the Australian gravitational-wave hunting team at <a href="https://www.ozgrav.org/">OzGrav</a>. OzGrav supports more than 100 scientists and engineers who are making critical contributions to improving LIGO instrumentation, data analysis software, and interpretation of the results.</p>
<h2>How far can LIGO see now?</h2>
<p>The recent upgrades of LIGO and Virgo mean astronomers can now detect gravitational waves from binary neutron star mergers further than ever before, up to 500 million light years away.</p>
<p>Any signals we detect from these distant mergers would have left their host galaxy around the time the first fish evolved on Earth (two hundred million years before dinosaurs came along).</p>
<p>Every second counts when astronomers are trying to use gravitational wave triggers to capture the last moments as neutron stars collide. </p>
<p>The team at the University of Western Australia node of OzGrav has developed a real-time search program (called “SPIIR”) to trigger gravitational waves from the LIGO-Virgo data within ten seconds. </p>
<p>The team has already identified four gravitational-wave candidates, and in the future it may even be possible to eventually alert astronomers before the emission of any light from a merger.</p>
<h2>Beating the noise</h2>
<p>An important part of the LIGO O3 upgrade was the installation of instruments called “quantum squeezers”. The squeezers are based on an Australian National University design and ANU OzGrav scientists were part of the team that installed and commissioned them.</p>
<p>One of the most significant engineering challenges in building LIGO is reducing noise that can drown out the miniscule gravitational-wave signals. This noise comes from many different sources, such as seismic noise from earthquakes, ocean waves and even vehicle traffic.</p>
<p>Another source of noise is quantum noise, due to the discrete nature of light. The squeezers dampen this quantum noise by changing the quantum properties of the light used by LIGO to detect ripples in the fabric of spacetime. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">LIGO team members (left-to-right: Fabrice Matichard, Sheila Dwyer, Hugh Radkins) install in-vacuum equipment as part of the squeezed-light upgrade.</span>
<span class="attribution"><span class="source">Nutsinee Kijbunchoo/ANU</span></span>
</figcaption>
</figure>
<h2>Another event detected</h2>
<p>With the third observing run now well underway, we’re already seeing the results of these improvements to LIGO instrumentation and software.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-we-found-a-white-dwarf-a-stellar-corpse-by-accident-114089">How we found a white dwarf – a stellar corpse – by accident</a>
</strong>
</em>
</p>
<hr>
<p>In addition to the technical improvements there’s another marked contrast with previous observing runs: all detections are being released to the astronomy community, and the wider public, straight away. </p>
<p>In the midst of the excitement about S190425z there was <a href="https://gracedb.ligo.org/superevents/S190426c/view/">another gravitational-wave alert</a> a day later - a candidate signal with properties that suggest it could be a merger of a neutron star and a black hole.</p>
<p>This was picked up by all three detectors but as yet we also have no host identified for this, so we are not yet sure of the nature of this event. But it’s another hint of the exciting results yet to come.</p><img src="https://counter.theconversation.com/content/116267/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney. She receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Eric Thrane works for Monash University. He receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Qi Chu works for the University of Western Australia. She receives funding from Australian Research Council.</span></em></p>The signal came in on ANZAC Day, ripples in space-time from the merger of two neutron stars an estimated 500-million light years away. But where it happened is still a mystery.Tara Murphy, Professor, University of SydneyEric Thrane, Associate professor, Monash UniversityQi Chu, Research fellow, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1079622018-12-03T13:06:06Z2018-12-03T13:06:06ZNew detections of gravitational waves brings the number to 11 – so far<figure><img src="https://images.theconversation.com/files/248354/original/file-20181203-194928-1wx57ti.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ripples in space-time caused by massive events such this artist rendition of a pair of merging neutron stars.</span> <span class="attribution"><span class="source">Carl Knox, OzGrav</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Four new detections of gravitational waves have been announced at the <a href="https://www.elisascience.org/news/conferences/gravitational-wave-physics-and-astronomy-workshop-gwpaw">Gravitational Waves Physics and Astronomy Workshop</a>, at the University of Maryland in the United States. </p>
<p>This brings the total number of detections to 11, since the first <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">back in 2015</a>.</p>
<p>Ten are from binary black hole mergers and one from the merger of two neutron stars, which are the dense remains of stellar explosions. One black hole merger was extraordinarily distant, and the most powerful explosion ever observed in astronomy.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-search-for-the-source-of-a-mysterious-fast-radio-burst-comes-relatively-close-to-home-105735">The search for the source of a mysterious fast radio burst comes relatively close to home</a>
</strong>
</em>
</p>
<hr>
<p>The latest news comes just a month after doubts were raised about the initial detection. In late October an article in New Scientist, headlined <a href="https://www.newscientist.com/article/mg24032022-600-exclusive-grave-doubts-over-ligos-discovery-of-gravitational-waves/">Exclusive: Grave doubts over LIGO’s discovery of gravitational waves</a>, raised the idea that it “might have been an illusion”. </p>
<p>So how confident are we that we are detecting gravitational waves, and not seeing an illusion?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s conception shows two merging black holes.</span>
<span class="attribution"><span class="source">LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)</span></span>
</figcaption>
</figure>
<h2>Open to scrutiny</h2>
<p>All good scientists understand that scrutiny and scepticism is the power of science. All theories and all knowledge are provisional, as science slowly homes in on our best understanding of the truth. There is no certainty, only probability and statistical significance. </p>
<p>Years ago the team searching for gravitational waves with the Laser Interferometer Gravitational-Wave Observatory (LIGO), determined the levels of statistical significance needed to make a claim of detection. </p>
<p>For each signal we determine the false alarm rate. This tells you how many years you would need to wait before you have an even chance of a random signal mimicking your real signal.</p>
<p>The weakest signal detected so far has a false alarm rate of one every five years, so still there is a chance that it could have been accidental. </p>
<p>Other signals are much stronger. For the three strongest signals detected so far you would have to wait from 1,000 times to 10 billion billion times the age of the universe for the signals to occur by chance.</p>
<h2>Knowing what to listen out for</h2>
<p>The detection of gravitational waves is a bit like acoustic ornithology.</p>
<p>Imagine you study birds and want to determine the population of birds in a forest. You know the calls of the various bird species. </p>
<p>When a bird call matches your predetermined call, you jump with excitement. Its loudness tells you how far away it is. If it was very faint against the background noise, you may be uncertain.</p>
<p>But you need to consider the <a href="https://wildambience.com/wildlife-sounds/superb-lyrebird/">lyre birds</a> that mimic other species. How do you know that sound of a kookaburra isn’t actually made by a lyre bird? You have to be very rigorous before you can claim there is a kookaburra in the forest. Even then you will only be able to be confident if you make further detections.</p>
<p>In gravitational waves we use memorised sounds called templates. There is one unique sound for the merger of each possible combination of black hole masses and spins. Each template is worked out using Einstein’s theory of gravitational wave emission.</p>
<p>In the hunt for gravitational waves, we are searching for these rare sounds using <a href="https://www.ligo.caltech.edu/page/facilities">two LIGO detectors</a> in the US and a third detector, <a href="http://public.virgo-gw.eu/language/en/">Virgo</a>, in Italy.</p>
<p>To avoid missing signals or claiming false positives, the utmost rigour is needed to analyse the data. Huge teams look over the data, search for flaws, criticise each other, review computer codes and finally review proposed publications for accuracy. Separate teams use different methods of analysis, and finally compare results.</p>
<p>Next comes reproducibility – the same result recorded again and again. Reproducibility is a critical component of science.</p>
<h2>The signals detected</h2>
<p>Before LIGO made its first public announcement of gravitational waves, two more signals had been detected, each of them picked up in two detectors. This increased our confidence and told us that there is a population of colliding black holes out there, not just a single event that could be something spurious.</p>
<p>The <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">first detected gravitational wave</a> was astonishingly loud and it matched a pre-determined template. It was so good that LIGO spent many weeks trying to work out if it was possible for it to have been a prank, deliberately injected by a hacker. </p>
<p>While LIGO scientists eventually convinced themselves that the event was real, further discoveries greatly increased our confidence. In August 2017 a signal was detected by the two LIGO detectors and the Virgo detector in Italy.</p>
<p>On August 17 last year a completely different, but long predicted type of signal was observed from a <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">coalescing pair of neutron stars</a>, accompanied by the predicted burst of gamma rays and light.</p>
<h2>The black hole mergers</h2>
<p>Now the LIGO-Virgo collaboration has completed the analysis of all the data since September 2015. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gmmD72cFOU4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The ten black hole mergers.</span></figcaption>
</figure>
<p>For each signal we determine the mass of the two colliding black holes, the mass of the new black hole that they create, and rather roughly, the distance and the direction. </p>
<p>Each signal has been seen in two or three detectors almost simultaneously (they were separated by milliseconds).</p>
<p>Eight of the 20 initial black holes have masses between 30 and 40 Suns, six are in the 20s, three are in the teens and only two are as low as 7 to 8 Suns. Only one is near 50, the biggest pre-collision black hole yet seen.</p>
<p>These are the numbers that will help us work out where all these black holes were made, how they were made, and how many are out there. To answer these big questions we need many more signals.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Graphic showing the masses of recently announced gravitational-wave detections and black holes and neutron stars.</span>
<span class="attribution"><span class="source">LIGO-Virgo / Frank Elavsky / Northwestern</span></span>
</figcaption>
</figure>
<p>The weakest of the new signals, GW170729, was detected on July 29, 2017. It was the collision of a black hole 50 times the mass of the Sun, with another 34 times the mass of the Sun.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">Explainer: why you can hear gravitational waves when things collide in the universe</a>
</strong>
</em>
</p>
<hr>
<p>This was by far the most distant event, having taken place, most likely, 5 billion years ago – before the birth of Earth and the Solar system 4.6 billion years ago. Despite the weak signal, it was the most powerful gravitational explosion discovered, so far. </p>
<p>But because the signal was weak, this is the detection with the false alarm rate of one every five years.</p>
<p>LIGO and Virgo are improving their sensitivity year by year, and will be finding many more events. </p>
<p>With planned new detectors we anticipate ten times more sensitivity. Then we expect to be detecting new signals about every five minutes.</p><img src="https://counter.theconversation.com/content/107962/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. He is affiliated with the Gravity Discovery Centre Foundation that operates an exciting self-funded education centre near Gingin, Western Australia where you can find out much more about black holes, neutron stars and gravitational waves. </span></em></p>More ripples in space-time have been detected from merging pairs of black holes, one of which was the most massive and distant gravitational-wave source ever observed.David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1054382018-10-24T13:33:24Z2018-10-24T13:33:24ZSupermassive black holes: we’ve spotted signs of mergers that may finally help us prove they exist<figure><img src="https://images.theconversation.com/files/241990/original/file-20181024-48718-1xt74j9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Visible light image of the radio galaxy Hercules A obtained by the Hubble Space Telescope superposed with a radio image taken by the Very Large Array of radio telescopes in New Mexico, USA.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Observations of nature tend to throw up unexpected results and new mysteries – whether you’re investigating the rain forest or outer space. When radio astronomy took off in the 1950s, we had no idea that it would lead to the discovery that galaxies including our own seem to have terrifyingly large black holes at their centre – millions to billions of times the mass of the sun. </p>
<p>A few decades later, we still haven’t been able to prove that these beasts – dubbed <a href="https://theconversation.com/how-we-caught-a-glimpse-of-a-supermassive-black-hole-having-a-meal-60736">supermassive black holes</a> – actually exist. But our new research, <a href="https://academic.oup.com/mnras/article/482/1/240/5105759">published in the Monthly Notices of the Royal Astronomical Society</a>, could one day help us do so.</p>
<p>Early radio astronomers discovered that some galaxies emit <a href="https://www.nasa.gov/directorates/heo/scan/communications/outreach/funfacts/txt_radio_spectrum.html">radio waves</a> (a type of electromagnetic radiation). They knew that galaxies sometimes collide and merge, and naturally wondered whether this <a href="http://adsabs.harvard.edu/full/1954ApJ...119..206B">could have something to do</a> with the radio emission. Better observations, however, <a href="https://academic.oup.com/mnras/article/166/3/513/2604753">refuted this idea over the years</a>. </p>
<p>They also discovered that the radio waves were emitted as <a href="http://adsabs.harvard.edu/full/1984ApJ...285L..35P">narrow jets</a>, meaning that the power came from a tiny region in the nucleus. The radio power was indeed huge – often surpassing the luminosity of all the stars in the galaxy taken together. Various suggestions were made as to how such a huge amount of energy could be produced, and it was in the 1970s that scientists <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev.aa.22.090184.002351">finally proposed</a> that a supermassive black hole could be the culprit. The objects are nowadays <a href="https://theconversation.com/filaments-that-bind-galaxies-together-illuminated-by-a-quasar-22146">known as quasars</a>.</p>
<p>Theoretical models estimated that these objects would have a mass of an entire small galaxy concentrated in a space comparable to Earth’s orbit around the sun.
But because only some galaxies produce energetic outbursts, it was unclear how common supermassive black holes would be. With the advent of the <a href="https://theconversation.com/telescopes-on-the-ground-may-be-cheaper-but-hubble-shows-why-they-are-not-enough-40724">Hubble Space Telescope</a> in 1990, the centres of nearby galaxies that did not emit radio bursts could finally be investigated. Did they contain supermassive black holes too?</p>
<p>It turned out that many did – astronomers saw signs of gravitating masses influencing the matter around it without emitting any light. Even the Milky Way showed evidence of having a supermassive black hole at the centre, now known as <a href="https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html">Sgr A*</a>. At this point, astronomers became increasingly convinced that supermassive black holes were a reality and could plausibly explain the extreme energetic outbursts from some galaxies.</p>
<p>However, there is no definitive proof yet. That is despite the fact that some supermassive black holes emit jets – these come from the surroundings of the black hole rather than the black hole itself. So how do you prove the existence of something completely dark? A black hole as defined by Einstein’s theory of general relativity is a region of space bounded by a horizon – a surface from inside of which no light or material object can ever escape. So, it’s a pretty difficult task for astronomers: they need to see something that emits nothing.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/241992/original/file-20181024-48715-bdlkx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Black hole collision and merger releasing gravitational waves.</span>
<span class="attribution"><span class="source">LIGO</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>For smaller black holes the size of a stellar mass, a proof was indeed found: when two such objects merge, <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">they emit gravitational waves</a>, a tiny wobbling of space that was for the first time registered in 2015. The detection proved that black holes exist, that they sometimes form pairs and that they indeed merge. This was a tremendous success, <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">honoured with the Nobel prize in 2017</a>.</p>
<p>We also have a good understanding of where normal sized black holes come from – they are what is left after a star much more massive than the sun has arrived at the end of its lifetime. But both the existence and the origin of supermassive black holes are shrouded in mystery.</p>
<h2>Spinning black holes</h2>
<p>We have now found indications that many of the radio jets produced by supermassive black holes may in fact be the result of these objects forming pairs, orbiting each other. We did this by comparing the observed radio maps of their regions with our computer models. </p>
<p>The presence of a second black hole would make the jets produced by the first one change direction in a periodic way over hundreds of thousands of years. We realised that the cyclic change in jet direction would cause a very specific appearance in radio maps of the galaxy centre.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/241988/original/file-20181024-48715-or0ofa.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lobes are created by the jets depositing energy to surrounding particles.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We found evidence of such a pattern in about 75% of our sample of “radio galaxies” (galaxies that emit radio waves), suggesting that supermassive black hole pairs are the rule, not the exception. Such pairs are actually expected to form after galaxies merge. Each galaxy contains a supermassive black hole, and since they are heavier than all the individual stars, they sink to the centre of the newly formed galaxy where they first form a close pair and then merge under emission of gravitational waves. </p>
<p>While our observation provides an important piece of evidence for the existence of pairs of supermassive black holes, it’s not a proof either. What we observe are still the effects that the black holes somehow cause indirectly. Just like with normal black holes, a full proof of the existence of supermassive black hole pairs requires detection of gravitational waves emitted by them.</p>
<p>Current gravitational wave telescopes can only detect gravitational waves from stellar mass black holes. The reason is that they orbit around one another much faster, which leads to the production of higher frequency gravitational waves that we can detect. The next generation of instruments will however be able to register low frequency gravitational waves as well – potentially from supermassive black hole pairs. This would finally prove their existence – half a century after they were first proposed. It’s an exciting time to be a scientist.</p><img src="https://counter.theconversation.com/content/105438/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Krause receives funding from Deutsche Forschungsgemeinschaft (DFG), Excellence Cluster Universe (Garching, Germany), European Science Foundation, Australian Research Council, International Space Science Institute (Bern, Switzerland), Ernst-Rudolf-Schloeßmann Stiftung (Max-Planck Society, Germany). </span></em></p>Merging supermassive black holes would emit gravitational waves, allowing scientists to detect them.Martin Krause, Senior Lecturer, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001552018-08-28T21:06:19Z2018-08-28T21:06:19ZNew era of astronomy uncovers clues about the cosmos<figure><img src="https://images.theconversation.com/files/231953/original/file-20180814-2894-1tzyen8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of two neutron stars spinning around each other while merging.</span> <span class="attribution"><span class="source"> NASA/CXC/Trinity University/D. Pooley et al.</span></span></figcaption></figure><p>Astronomers have had a blockbuster year. </p>
<p>In addition to tracking down <a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">a cosmic source of neutrinos</a>, they have detected the merger of <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">two city-sized neutron stars, each more massive than the sun</a>. </p>
<p>The <a href="https://www.ligo.org/science/Publication-GW170817MMA/">discoveries were heralded</a> as evidence that a “<a href="https://www.ligo.org/science/Publication-GW170817MMA/">new era of multimessenger astronomy</a>” had arrived. </p>
<p>But what is multimessenger astronomy? </p>
<p>In our daily lives, we interpret the world around us based on different signals, such as sound waves, light (a type of electromagnetic wave) and skin pressure. Each of these signals may be carried by a different “messenger.” New messengers lead to new insights. So astronomers have eagerly welcomed a new set of messengers to their science.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Twenty-seven radio antennas make up the Karl G. Very Large Array in New Mexico. The VLA is an important tool for studying cosmic radio waves.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Many messengers</h2>
<p>For most of the history of astronomy, scientists primarily studied signals transmitted by one messenger, electromagnetic radiation. These waves, which move through space and time, are described by their wavelengths or the amount of energy found in their particles, the photons.</p>
<p>Radio waves have photons with the lowest amount of energy and the longest wavelengths, followed by infrared and optical light at intermediate energies and wavelengths. X-rays and gamma-rays have the shortest wavelengths and the highest energy. </p>
<p>But scientists study others messengers too: </p>
<ul>
<li>Cosmic rays: charged atomic particles and nuclei travelling near the speed of light.</li>
<li>Neutrinos: uncharged particles that see most of the universe as transparent.</li>
<li>Gravitational waves: wrinkles in the very fabric of space and time.</li>
</ul>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The four messengers of astronomy.</span>
<span class="attribution"><span class="source">Adapted from IceCube Collaboration</span></span>
</figcaption>
</figure>
<p>And while some fields in astronomy have explored these messengers for years, astronomers have only recently observed events from well beyond the Milky Way with more than one messenger at the same time. In just a few months, the number of sources where astronomers can piece together the signals from different messengers doubled.</p>
<h2>Like a walk on the beach</h2>
<p>Multimessenger astronomy is a natural evolution of astronomy. Scientists need more data to put together a complete picture of the objects they study and match the theories they develop with their observations. </p>
<p>Astronomers have combined different wavelengths of photons to piece together some of the mysteries of the universe. For example, the combination of radio and optical data played a major role in determining that the Milky Way is a spiral galaxy in 1951.</p>
<p>And astronomy continues to reveal great results about our universe using just one messenger, photons. So if multimessenger astronomy is just an evolutionary step of an incredible history of successes, does that mean it’s just a new buzzword?</p>
<p>We don’t think so.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artistic rendition of NASA’s Chandra X-ray Observatory. This space satellite produces the most detailed X-ray images of high energy astrophysical phenomena.</span>
<span class="attribution"><span class="source">NGST</span></span>
</figcaption>
</figure>
<p>Imagine you are walking along an ocean beach. You are enjoying the sight of an incredible sunset, hearing the rolling waves, feeling the sand beneath your feet and smelling the salty air. Your combined senses form a more complete experience. </p>
<p>With multimessenger astronomy, we hope to learn more from the universe by combining multiple messengers, just as we combine sight, hearing, touch and smell.</p>
<h2>But it’s not always a picnic</h2>
<p>The cultures of astronomers and particle physicists represent different approaches to science. In multimessenger astronomy, these cultures collide.</p>
<p>Astronomy is an observational field and not an experiment. We study astronomical objects that change over time (time-domain astronomy), which means we often have only one chance to observe a transient astronomical event.</p>
<p>Until recently, most time-domain astronomers worked in small teams, on many projects at once. We use resources like <a href="http://www.astronomerstelegram.org/">The Astronomer’s Telegram</a> or the <a href="https://gcn.gsfc.nasa.gov/">Gamma-ray Coordination Network</a> to rapidly communicate results, even before submitting scientific papers.</p>
<p>Since most of the expected sources of multimessenger signals are transient astronomical events, it’s a huge effort to capture the messengers besides photons.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">The IceCube observatory detects neutrino and discovers a blazar as its source</a>
</strong>
</em>
</p>
<hr>
<p>Particle physicists have led the way in creating large international collaborations to tackle their hardest problems, including the <a href="https://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>, the <a href="https://icecube.wisc.edu/">IceCube Neutrino Observatory</a> and the <a href="https://www.ligo.caltech.edu/">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a>. Corralling hundreds to thousands of researchers to work towards common goals requires comprehensive identification of roles, strict communication guidelines and many teleconferences.</p>
<p>The need to respond to rapid changes in a multimessenger source and the huge effort to capture multimessenger signals means astronomy and particle physics must merge towards one another to elicit the best of both cultures.</p>
<h2>The benefits of multimessenger astronomy</h2>
<p>While multimessenger astronomy is an evolution of what astronomers and particle physicists have done for decades, the combined results are intriguing.</p>
<p>The detection of gravitational waves from merging neutron stars confirmed that <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">these collisions made a large fraction of the gold and platinum</a> on Earth (and throughout the universe). It also showed how these collisions give rise to (at least some) <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">short gamma-ray bursts</a> — the origin of these explosive events has been a huge open question in astronomy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The IceCube Neutrino Observatory used a cubic kilometre of crystal-clear Antarctic ice to capture the signal of a rare neutrino that helped pinpoint a galaxy four billion light years away with a supermassive black hole launching a jet of photons and near light-speed particles directly at our Solar System.</span>
<span class="attribution"><span class="source">IceCube Collaboration/NSF</span></span>
</figcaption>
</figure>
<p>The first association of a neutrino with a single astronomical source provided a glimpse into how the universe makes its most energetic particles. Multimessenger astronomy is revealing details about some of the most extreme conditions in our universe.</p>
<p>The multimessenger perspective is already yielding more than the sum of its parts — and we can expect to see more surprising discoveries in the future. Elite teams across Canada are already contributing to the growth of this young field, and multimessenger astronomy promises to play a major role in our next decade of astronomical research in Canada — and across the world.</p><img src="https://counter.theconversation.com/content/100155/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gregory Sivakoff receives funding from Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), and Alberta Economic Development and Trade (EDT). Gregory Sivakoff is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Gregory Sivakoff also serves on the Council of the American Association of Variable Star Observers (AAVSO), a non-profit citizen astronomy organization.
</span></em></p><p class="fine-print"><em><span>Daryl Haggard receives funding from the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholars Program, Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du Québec – Nature et technologies (FRQNT). Daryl Haggard is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Daryl Haggard also serves on the Laser Interferometer Gravitational-Wave Observatory (LIGO) Program Advisory Committee.</span></em></p>Astronomers are now able to detect a host of signals streaming through the universe. This newfound ability is like gaining new senses and it’s opening the door to understanding the cosmos.Gregory Sivakoff, Associate Professor, University of AlbertaDaryl Haggard, Assistant Professor of Physics, McGill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/970442018-08-21T10:32:47Z2018-08-21T10:32:47ZSwift’s telescope reveals birth, deaths and collisions of stars through 1 million snapshots in UV<figure><img src="https://images.theconversation.com/files/221208/original/file-20180531-69481-kmpc6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Technicians prepare Swift's UVOT for vibration testing on Aug. 1, 2002, more than two years before launch, in the High Bay Clean Room at NASA's Goddard Space Flight Center in Greenbelt, Md.
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/swift/bursts/swift-images.html">NASA's Goddard Space Flight Center </a></span></figcaption></figure><p>Imagine if the color camera had never been invented and all our images were in black and white. The world would still look beautiful, but incomplete. For thousands of years, that was how humans saw the universe. On Earth, we can only see part of the light that stars emit.</p>
<p>Much of what we can’t see – in the infrared, the ultraviolet, the X-ray and the gamma ray wavelengths – is blocked by the Earth’s atmosphere. For the most part, this is a good thing. The atmosphere traps infrared light keeping the Earth warm at night and blocks high-energy ultraviolet light, X-rays and gamma rays, keeping us safe from deadly cosmic radiation, while letting in visible portions of the spectrum of light. For astronomers, however, this has a drawback: We look at the universe with one eye shut, unable to receive all of the information the universe is sending to us.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=225&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=225&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=225&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=282&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=282&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=282&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Visible light is just a tiny part of the electromagnetic spectrum.</span>
<span class="attribution"><a class="source" href="https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_compare_level1_lg.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Launched on November 20, 2004, and orbiting an altitude of 340 miles, NASA’s <a href="https://swift.gsfc.nasa.gov">Neil Gehrels Swift Observatory</a> has three telescopes that monitor the universe using wavelengths of light that are blocked by Earth’s atmosphere. These included the X-Ray Telescope, the gamma-ray-sensitive Burst-Alert Telescope and the Ultraviolet Optical Telescope (UVOT). The UVOT recently delivered its 1 millionth image – data that astrophysicists like me use to gain insights into everything from the origins of the universe to the chemical composition of nearby comets.</p>
<h2>Watching the birth of black holes</h2>
<p>Swift’s primary mission is to study the afterglow of gamma ray bursts (GRBs) – which document the birth of black holes. Black holes are forged in the most violent explosions in the universe – the explosion of a massive star or the merging of two neutron stars (the shriveled husks left over from past stellar explosions). These explosions are so powerful – producing tens to hundreds of billions of times more energy than the sun – that even though they occur billions of light years away from Earth, they can still be detected by instruments like Swift. In fact, the first GRBs were detected by the <a href="https://heasarc.gsfc.nasa.gov/docs/heasarc/missions/vela5a.html">Vela satellites</a>, which were built to detect the explosions of nuclear weapons. </p>
<p>Over nearly 14 years, Swift has studied over a thousand GRBs. In doing so, it has revealed what powers them and given us glimpses into the furthest reaches of the cosmos, to the time when the first stars were being formed after the Big Bang.</p>
<p>However, one of the things you learn working on a space telescope mission is that if you build it, they will come. The mission provides capabilities to the community of astrophysicists – simultaneous X-ray/UV imaging and a rapid response to requests to observe and photograph specific sections of the sky – which are only available to Swift. We can focus our telescopes on an object of interest within hours of a “Target of Opportunity” request through our website, something no other mission can do. UVOT also fills an important niche by observing larger areas of the sky than can be observed with the more powerful UV instruments aboard the <a href="https://www.nasa.gov/mission_pages/hubble/main/index.html">Hubble Space Telescope</a>. These capabilities have proved a boon to the community and enabled study all sorts of objects and phenomenon beyond GRBs. </p>
<h2>Swift’s ultraviolet-aided discoveries</h2>
<p>Nearby galaxies are full of activity with new stars being formed. Swift is able to capture panoramic ultraviolet images that highlight the youngest, most massive stars in these galaxies. This gives us insight into what the universe has been doing over the last few hundred million years. My research team’s work has focused on nearby galaxies – like Andromeda and the Magellanic Clouds – to reveal what processes drive their past and ongoing star formation.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=298&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=298&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=298&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=374&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=374&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=374&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left is an image of the nearby galaxy NGC 3623 taken with UV. On the right is an optical image. Note how the galaxies spiral arms — where new stars are being born — stand out in the ultraviolet wavelengths emitted by these hot objects.</span>
<span class="attribution"><span class="source">NASA/Swift/L.McCauley, PSU</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>With UVOT, we get a much better view of supernova explosions. These can occur when a white dwarf, the remnant of a star like the sun, explodes, or during the final death throes of a massive star, more than eight times the mass of the sun. These events generate enormous amounts of ultraviolet light, and Swift has a unique ability to observe them within hours of discovery. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left is an ultraviolet composite made from several images of the Whirpool Galaxy (M51) taken between 2005-2007. The image on the right was made in June 2011, shortly after astronomers detected the explosion of a massive star in one of the galaxy’s outer spiral arms. The object is marked by the red circle.</span>
<span class="attribution"><span class="source">NASA/Swift/E. Hoversten, PSU</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Comets sweep through our solar system, transforming from a frozen solid ball to a vapor as they approach the sun and creating magnificent tails of ionized particles. Swift studies these comets, and analyzes their chemical composition by breaking the light they emit into different wavelengths. Swift also allows scientists to measure a comet’s rotation by seeing how the light changes over time. This has revealed that violent eruptions on the comet surface can dramatically alter a comet’s path. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=680&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=680&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=680&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This image of Comet Lulin was taken by Swift on January 28, 2009. It shows data obtained by Swift’s Ultraviolet/Optical Telescope (blue and green) and X-Ray Telescope (red). The image of the star field (white) was acquired by the Digital Sky Survey. At the time of the observation, comet Lulin was 99.5 million miles from Earth and 115.3 million miles from the sun. The ultraviolet light comes from hydroxyl molecules and shows that, at this time, Lulin was shedding 800 gallons of water every second.</span>
<span class="attribution"><span class="source">D. Bodewits/Swift/NASA</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>One of the most exciting discoveries that Swift made was connected with the recent discovery of gravitational waves by the <a href="https://losc.ligo.org/detector_status/">Laser Interferometer Gravitational-Wave Observatory</a> (LIGO). Gravitational waves are distortions in the fabric of spacetime created by the motions of extremely massive objects. In August of 2017, two neutrons stars collided in a distant galaxy, creating gravitational waves powerful enough to be detected on Earth. Swift was one of an army of telescopes that looked for the source of the gravitational waves. The mad scramble over those few days led to one of the most exciting discoveries of the last decade – a luminous afterglow from the source of the gravitational waves. This has opened up new branches of science by connecting a new way of studying the universe – through gravitational waves – to the traditional way – through light.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=669&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=669&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=669&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artist’s depiction of a space warping collision of two merging neutron stars. The ripples represent the gravitational waves that distort the space-time grid. The narrow beams shooting out of the collision show the gamma rays burst that are released after the gravitational waves. The yellow clouds glow with other wavelengths of light that are generated in the collision.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/page/press-release-gw170817">NSF/LIGO/Sonoma State University/A. Simonnet</a></span>
</figcaption>
</figure>
<p>UVOT has been taking snapshots of the universe since 2004 and finally piled up its millionth image. Its success is a testament to the international team of engineers, scientists and staff at the three institutions that support it – the <a href="http://www.psu.edu">Pennsylvania State University</a>; <a href="http://www.ucl.ac.uk/mssl/">Mullard Space Science Laboratory</a> in Surrey, England; and NASA’s <a href="https://www.nasa.gov/goddard">Goddard Space Flight Center</a> in Greenbelt, Maryland. It has been my privilege to be a part of this team for the last nine years. What does the future hold for UVOT? We hope to find more sources of gravitational waves, survey nearby galaxies, study even more supernovae, and monitor how objects in the universe change over time.</p>
<p>Here’s to the next million images.</p><img src="https://counter.theconversation.com/content/97044/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Siegel is a Research Professor at Pennsylvania State University and receives research funding from NASA.</span></em></p>The Swift Observatory passed a milestone: 1 million snapshots of the universe. These exquisite and revealing pictures have captured the births and deaths of stars, gravitational waves and comets.Michael Siegel, Research Professor of Astronomy and Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1003822018-08-16T20:17:50Z2018-08-16T20:17:50ZWe’re going to get a better detector: time for upgrades in the search for gravitational waves<figure><img src="https://images.theconversation.com/files/231640/original/file-20180813-2915-1w3rsut.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's depiction of a pair of neutron stars colliding.</span> <span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/WA/news/ligo20171016">NASA/Swift/Dana Berry</a></span></figcaption></figure><p>It’s been a year since <a href="https://www.ligo.caltech.edu/page/what-are-gw">ripples in space-time</a> from a <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">colliding pair of dead stars</a> tickled the gravitational wave detectors of the <a href="https://www.ligo.caltech.edu">Advanced LIGO</a> and <a href="http://public.virgo-gw.eu/language/en/">Advanced Virgo</a> facilities. </p>
<p>Soon after, astronomers around the world began a <a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">campaign</a> to observe the <a href="https://theconversation.com/we-beat-a-cyber-attack-to-see-the-kilonova-glow-from-a-collapsing-pair-of-neutron-stars-85660">afterglow</a> of the collision of a binary <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">neutron star</a> merger in radio waves, microwaves, visible light, x-rays and more.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">Explainer: what is a neutron star?</a>
</strong>
</em>
</p>
<hr>
<p>This was the dawn of <a href="https://arxiv.org/abs/1606.09335">multi-messenger astronomy</a>: a new era in astronomy, where events in the universe are observed with more than just a single type of radiation. In this case, the messengers were gravitational waves and electromagnetic radiation. </p>
<h2>What we’ve learned (so far)</h2>
<p>From this single event, we learned an incredible amount. Last October, on the day the detection was made public, 84 scientific papers were published (or the preprints made available). </p>
<p>We learned that <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa920c">gravity and light travel at the same speed, neutron star mergers are a source of short gamma-ray bursts</a>, and that kilonovae – the explosion from a neutron star merger – are <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">where our gold comes from</a>. </p>
<p>This rich science came from the fact that we were able to combine our observatories to witness this single event from multiple astronomical “windows”. The gravitational waves arrived first, followed 1.7 seconds later by gamma-rays. That is a pretty small delay, considering the waves had been travelling for 130 million years. </p>
<p>Over the next few weeks, visible light and radio waves began to be observed and then <a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">slowly faded</a>. </p>
<p>It seemed like the news about gravitational waves was coming fast and furious, with the <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">first detection announced in 2016</a>, a <a href="https://theconversation.com/an-award-with-real-gravity-how-gravitational-waves-attracted-a-nobel-prize-66491">Nobel prize in 2017</a>, and the announcement of the binary neutron star merger just weeks after the Nobel prize.</p>
<h2>Time for upgrades</h2>
<p>On this first anniversary of the neutron star merger, the gravitational wave detectors are offline for upgrades. They actually went offline shortly after the detection and will come back online some time early in 2019. </p>
<p>The work of making gravitational wave detectors function requires extraordinary patience and dedication. These are exquisite experiments – it took more than 40 years of technological development by a community of more than a thousand scientists to get to the point of detecting the first signal.</p>
<p>Naturally, improving on this work is not easy. So what does it actually take?</p>
<p>We really do <a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">listen to gravitational waves</a>, and our detectors act more like microphones than telescopes or cameras. </p>
<p>If you listen to the first ever gravitational wave signal (below) you can hear the wave-chirp itself, accompanied by a rumbling hiss (the audio is shifted to a higher frequency to make it easier to hear). </p>
<p><audio preload="metadata" controls="controls" data-duration="4" data-image="" data-title="The first gravitational wave signal." data-size="23222" data-source="LIGO Open Science Center" data-source-url="" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1251/gw150914-h1-shifted.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
The first gravitational wave signal.
<span class="attribution"><span class="source">LIGO Open Science Center</span><span class="download"><span>22.7 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/1251/gw150914-h1-shifted.m4a">(download)</a></span></span>
</div></p>
<p>That hiss is noise in our detector. It’s what limits our ability to find gravitational waves, and it also limits our ability to infer properties about their sources. </p>
<p>It’s a bit like if you’re standing in the kitchen and you want listen to birds singing outside, but you can’t really hear them because the dishwasher is running too loudly. </p>
<h2>Quiet please!</h2>
<p>To detect gravitational waves, we need to do more than just turn off the dishwasher. We need to build the quietest, <a href="https://arxiv.org/abs/1604.00439">best-isolated thing on Earth</a>. </p>
<p>If we could eliminate the noise in our detectors entirely, the gravitational wave chirp would sound like this (again, the audio is shifted to a higher frequency to make it easier to hear): </p>
<p><audio preload="metadata" controls="controls" data-duration="0" data-image="" data-title="A theoretical, noiseless version of the first gravitational wave signal (GW150914)." data-size="6072" data-source="" data-source-url="" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1252/gw150914-nr-shifted.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
A theoretical, noiseless version of the first gravitational wave signal (GW150914).
</div></p>
<p>Unfortunately, the laws of quantum mechanics and thermodynamics both prevent us from eliminating the noise entirely. Nonetheless, we strive to do the best that these fundamental limits permit. This involves, among many other extraordinary things, <a href="https://www.ligo.caltech.edu/mit/video/ligo20170216v">hanging our mirrors on glass threads</a> . </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Before sealing up the chamber and pumping the vacuum system down, a LIGO optics technician inspects one of LIGO’s core optics (mirrors) by illuminating its surface with light at a glancing angle.</span>
<span class="attribution"><span class="source">Matt Heintze/Caltech/MIT/LIGO Lab</span></span>
</figcaption>
</figure>
<p>Our mirrors weight 40kg each and are suspended from four of these glass threads, which are less than a half-millimetre in diameter and exquisitely crafted.</p>
<p>The threads are under enormous stress, and the slightest imperfection (or the slightest touch) can cause them to explode.</p>
<p>Just such an explosion happened earlier this year while installing a new mirror. Fortunately, the precious mirror fell into a cradle designed for just such a possibility, and was not damaged. </p>
<p>Nonetheless, the delicate, intricate work of creating the glass threads, attaching them to the mirror, hanging the mirror and then installing it all needed to be redone. </p>
<h2>Improvements to the detector</h2>
<p>This was a heartbreaking setback for the team, but the added delay was not entirely in vain. In parallel with remaking the glass threads and rehanging the new mirror, we made some other improvements to the detector, for which we otherwise would not have had enough time. </p>
<p>One of the goals of this upgrade period is to install something called a quantum squeezed light source into the gravitational wave detectors.</p>
<p>As mentioned earlier, quantum mechanics mandates a certain minimum amount of noise in any measurement. We can’t arbitrarily reduce this quantum noise, but we can move it around and change its shape by <em>squeezing</em> it.</p>
<p>This is a bit like sweeping dust under the rug. It’s not really gone, but it might not bother you so much anymore. The quantum squeezed light source does just this. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=258&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=258&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=258&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=324&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=324&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=324&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Australian National University scientists Nutsinee Kijbunchoo and Terry McCrae build components for a quantum squeezed light source at LIGO Hanford Observatory in Washington, US.</span>
<span class="attribution"><span class="source">Nutsinee Kijbunchoo</span></span>
</figcaption>
</figure>
<p>A gravitational wave detector is already a very complex system, and a squeezed light source is another complex system, so putting them together can be a challenge. </p>
<p>Despite the complexity of this challenge, when the squeezed light source was activated for the first time at the LIGO detector in Livingston, Louisiana, US, in February this year there was an immediate improvement in the quantum noise: the gravitational wave detector output got just a bit quieter.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/einsteins-theory-of-gravity-tested-by-a-star-speeding-past-a-supermassive-black-hole-100658">Einstein’s theory of gravity tested by a star speeding past a supermassive black hole</a>
</strong>
</em>
</p>
<hr>
<p>Much tuning remains to be done to get the detectors in optimal shape, but it is a real delight when something so complex goes well right from the start. </p>
<p>With these first detections, we have begun to explore the population of black holes in the universe, heard the merger of neutron stars, and
<a href="https://arxiv.org/abs/1712.03240">probably witnessed the birth of a new black hole</a>. </p>
<p>With the upgrades under way, we will study these objects with better clarity, hopefully understand where they came from, and maybe even find something completely new and unexpected.</p><img src="https://counter.theconversation.com/content/100382/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Ward receives funding from the Australian Research Council. </span></em></p>To better detect gravitational waves, we need to build the quietest and most isolated thing on Earth. And make sure we don’t drop those 40kg mirrors.Robert Ward, Associate Investigator, OzGrav (ARC Centre of Excellence for Gravitational Wave Discovery), Research Fellow in Physics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/942942018-04-30T20:15:47Z2018-04-30T20:15:47ZSignals from a spectacular neutron star merger that made gravitational waves are slowly fading away<figure><img src="https://images.theconversation.com/files/215476/original/file-20180418-134691-1ijq629.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Neutron star merger.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">Credit: NASA's Goddard Space Flight Center/CI Lab</a></span></figcaption></figure><p>Eight months ago, the <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">detection of gravitational waves</a> from a binary neutron star merger had us and other astronomers around the world rushing to observe one of the most energetic events in the universe. </p>
<p>What most people don’t realise is that we continued to observe the event every few weeks from then up to now. </p>
<p>Our team <a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">started searching for radio emission from the merger</a>, <a href="https://www.ligo.caltech.edu/page/press-release-gw170817">known as GW170817</a>, making a detection two weeks after the August event. Now, the radio emission is starting to fade. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">After the alert: radio 'eyes' hunt the source of the gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>As we prepare to say goodbye (at least for now) to this incredible object, we reflect on what what we’ve learned so far, with <a href="https://arxiv.org/abs/1803.06853" title="A turnover in the radio lightcurve of GW170817">our paper accepted for publication</a> in the Astrophysical Journal. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Radio observations of GW170817 from two telescopes. The central bright object in each image is the host galaxy NGC 4993. The smaller bright spot in the crosshairs is the neutron star merger.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/nature25452">David Kaplan. Data from Mooley et al. (2018), Nature, 554, 207</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The detection of gravitational waves and electromagnetic radiation (such as light and radio waves) from the same object mean physicists have been able to:</p>
<ul>
<li><p>confirm a prediction of general relativity that <a href="https://www.ligo.org/science/Publication-GW170817GRB/index.php">gravitational waves travel at the speed of light</a></p></li>
<li><p>figure out <a href="https://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">how matter behaves when you squeeze it</a> harder than in the nucleus of an atom</p></li>
<li><p><a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">explain</a> where some of the gold (and other heavy elements) in the universe are produced</p></li>
<li><p>and start to solve a decades-old mystery about <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">what causes short gamma-ray bursts</a>.</p></li>
</ul>
<h2>Observing the merger</h2>
<p>Radio telescopes such as the <a href="https://www.narrabri.atnf.csiro.au/public/">Australia Telescope Compact Array</a> and the <a href="http://www.vla.nrao.edu/">Jansky Very Large Array</a> (in the United States) are designed to detect electromagnetic radiation with wavelengths from centimetres to metres.</p>
<p>Unlike visible light, radio waves travel through space almost unimpeded by dust. They can be detected during the day as well as at night: radio telescopes can observe around the clock.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/1hawK5JwVfY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Timelapse of the CSIRO’s Australia Telescope Compact Array. Credit: Alex Cherney (terrastro.com)</span></figcaption>
</figure>
<p>The radio waves we detected have travelled 130 million light years from the galaxy <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NGC+4993">NGC 4993</a> where the neutron star merger took place. </p>
<p>When the two neutron stars collided they emitted a burst of gamma rays shortly after, which was detected by the Fermi satellite 1.74 seconds after the gravitational waves. What happened next in the explosion is what we’ve all been trying to work out.</p>
<p>Within 12 hours astronomers had detected a bright, fading signal in visible light. We think this came from neutron star material flung out at 50% of the speed of light. It was glowing hot from a bunch of radioactive decays. </p>
<p><a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">Neutron stars</a> are the most dense objects we know of, except for black holes: imagine the Sun squashed into a region the size of a city. </p>
<p>When two neutron stars collide they form a new object that has slightly less mass than the two original stars: in this case likely a new black hole. A tiny fraction of the mass is blasted out as both matter and energy (remember E=mc<sup>2)</sup> and that is what we detect on Earth.</p>
<h2>What do radio waves tell us?</h2>
<p>The radio emission we detected days later, though, is a different matter.</p>
<p>Radio waves are created when electrons are accelerated in magnetic fields. This happens at shock fronts in space, as material from stellar explosions crashes into the stuff around the star. </p>
<p>This stuff is called the interstellar medium and is about 10 quintillion times less dense than air on Earth (almost, but not quite, a vacuum). The nature of the radio waves tells us the details of this shock, which we can run backward in time to try to understand the explosion. </p>
<p>One big question is whether there was a narrow jet of material moving at 99.99% of the speed of light that punched its way out of the explosion and hit the interstellar medium.</p>
<p>We think that these must happen in gamma-ray bursts: did that happen here? </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/p2Ab26gnQ1g?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A simulation of a neutron-star merger giving rise to a broad outflow – a ‘cocoon’. A cocoon is the best explanation for the radio waves, gamma rays and X-rays the astronomers saw arising from the neutron-star merger GW170817.</span></figcaption>
</figure>
<h2>What happened in the explosion?</h2>
<p>We’re still not sure of the details, but we don’t think there was a successful jet in GW170817. That’s because we have now observed the radio emission start to fade (the optical emission started to fade immediately).</p>
<p>This shows the explosion probably isn’t a classic gamma-ray burst with relativistic jets, as shown in the figure below (left). What is more likely is that we are seeing a “cocoon” of material that has broken out from the explosion. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Models of what might be happening in the merger. Our data has shown the left option is unlikely, and the radio emission is probably caused by a cocoon of material (right).</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/content/358/6370/1559">Reprinted with permission from Kasliwal et al., Science (2017)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>So where does this material come from?</p>
<p>The material flung out of the neutron stars (known as ejecta) was moving fast, about 50% of the speed of light. What if there was an even faster (99.99% of the speed of light) jet that happened soon after?</p>
<p>This jet could have blown a bubble in the ejecta, making it move faster (maybe 90% of the speed of light) and stopping the jet in its tracks: we call this a cocoon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Radio observations of the neutron star merger show that it is now fading.</span>
<span class="attribution"><a class="source" href="https://arxiv.org/abs/1803.06853">David Kaplan, Dougal Dobie. Data from Dobie et al. (2018), ApJL</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Saying goodbye (for now)</h2>
<p>After eight months of watching GW170817 we know that it is different to anything we’ve seen before, and has behaved in completed unexpected ways.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/captured-radio-telescope-records-a-rare-glitch-in-a-pulsars-regular-pulsing-beat-94815">Captured! Radio telescope records a rare 'glitch' in a pulsar's regular pulsing beat</a>
</strong>
</em>
</p>
<hr>
<p>The radio emission is now fading, but this may not be the end of the story. Most models predict a long term afterglow from neutron star mergers, so GW170817 might reappear months or even years in the future.</p>
<p>In the meantime, we are waiting with anticipation for the <a href="https://www.ligo.caltech.edu/">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a> to start its next observing run early next year. We might even capture a new type of event, a neutron star merging with a black hole.</p><img src="https://counter.theconversation.com/content/94294/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney. She receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>David Kaplan works for the University of Wisconsin-Milwaukee, and he receives funding from the US National Science Foundation.</span></em></p>Astronomers are getting ready to say good bye to the radio emission from a neutron star merger – one of the most energetic events in the universe – that was detected last year.Tara Murphy, Associate Professor and ARC Future Fellow, University of SydneyDavid Kaplan, Associate professor of Physics, University of Wisconsin-MilwaukeeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/923562018-03-12T19:05:48Z2018-03-12T19:05:48ZExplainer: why you can hear gravitational waves when things collide in the universe<figure><img src="https://images.theconversation.com/files/209273/original/file-20180307-146675-1ki0syv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ns gw art</span> </figcaption></figure><p>Whenever there’s an announcement of a new discovery of gravitational waves there is usually an accompanying sound, such as this:</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TWqhUANNFXw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The sound of first gravitational waves detected.</span></figcaption>
</figure>
<p>We have only detected half a dozen signals so far. The first five are black holes whose chirp signal is extremely brief. The last one is the sound of <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">a pair of neutron stars</a> spiralling together. This signal lasted more than a minute.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/WoDCPTLgxh4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Listen for the chirp.</span></figcaption>
</figure>
<p>With good earphones (and good ears) you may be able to hear the lower frequencies but the final chirp is unmistakable. A friend commented that the sound is like the call of the Australian whip bird.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
</strong>
</em>
</p>
<hr>
<p>So what is this sound? Are we really <em>hearing</em> gravitational waves?</p>
<p>To answer that it helps to think about other devices that detect waves, such as seismometers.</p>
<h2>Listening for an earthquake</h2>
<p>Today a worldwide network of seismometers listens to the Earth as it continuously vibrates. You can hear some <a href="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php">examples of earthquakes online at the US Geological Survey</a> (USGS).</p>
<p><audio preload="metadata" controls="controls" data-duration="9" data-image="" data-title="The 1992 Magnitude 7.3 Landers Earthquake" data-size="112478" data-source="United States Geological Survey" data-source-url="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1074/mtcm.mp3" type="audio/mpeg">
</audio>
<div class="audio-player-caption">
The 1992 Magnitude 7.3 Landers Earthquake.
<span class="attribution"><a class="source" rel="nofollow" href="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php">United States Geological Survey</a><span class="download"><span>110 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/1074/mtcm.mp3">(download)</a></span></span>
</div></p>
<p>Behind the idea of the <a href="https://earthquake.usgs.gov/learn/glossary/?term=seismograph">seismometer</a> is inertia: the linking of mass to space. You feel inertia when you push a car. The more massive the car, the more slowly it speeds up. Inertia resists changes in the motion of matter through space. </p>
<p>In a seismometer a large, delicately suspended mass is freed from most forces, so its inertia links it to space. In an earthquake the ground suddenly shakes. If you feel an earthquake you are feeling sudden changes in your motion through space.</p>
<p>In the seismometer the suspended mass stays still because of its inertia, but the frame of the seismometer follows the shaking Earth. From inside the seismometer it seems as if the mass has suddenly moved.</p>
<h2>Can you hear it?</h2>
<p>Sound is a wave of vibration that we normally hear passing through the air, but we can also hear under water and through solids. <a href="https://www.britannica.com/science/seismic-wave">Seismic waves</a> are waves of vibration passing through the solid Earth and this is what is picked up by modern seismometers. </p>
<p>If you were to insist that sound must be audible to us humans, then we can’t actually hear most earthquakes. This is because the vibration frequency is usually lower than the frequency threshold of human hearing.</p>
<p>But record it and speed up the playback and you can hear symphonies of seismic sounds like those you can <a href="https://earthquake.usgs.gov/learn/topics/listen/">listen to here at the USGS</a>.</p>
<p>Gravitational waves are waves of stretching and shrinking space. Like seismometers, gravitational wave detectors use the principle of inertia, but in this case the action is reversed. Space expands and shrinks and inertia causes suspended masses to follow.</p>
<p>Motions of space cannot be detected at a single location, for the same reason you cannot measure the stretching of an elastic band at a single point. But a <em>pair</em> of separated masses will become closer together if space shrinks, and further apart if space expands. Inertia makes the masses follow space, but neither mass feels a force.</p>
<p>Similarly, the expansion of space in the universe, that proved the Big Bang theory, causes all the galaxies to be moving apart without any force driving them. But gravitational waves are different in one respect: they simultaneously stretch in one direction and shrink the perpendicular direction. </p>
<p>In essence, gravitational waves vibrate the spacing between masses. The effects are tiny, so each mass must be exquisitely suspended so that it is not affected by the vibrations of the ground, and held in vacuum so that sounds in the air do not affect them.</p>
<h2>The big breakthrough</h2>
<p>It took 50 years of technology development before we had enough sensitivity to measure these waves. The masses we use are 40kg mirrors and lasers are used to measure their spacing.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tQ_teIUb3tE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Gravitational waves cause he mirrors to move.</span></figcaption>
</figure>
<p>Albert Einstein’s theory of <a href="https://theconversation.com/au/topics/general-relativity-161">general relativity</a> tells us that space and time are elastic. Spacetime is an elastic medium that is actually a billion billion billion times stiffer than steel. </p>
<p>We are constantly moving freely through this elastic medium, but we have to apply forces using muscles or tires or rocket engines to allow us to overcome the principle of inertia, thereby <em>changing</em> our motion through space as we have to when we move around relative to other objects.</p>
<p>If a pair of black holes orbit each other they make enormous deformations in the shape of space around them, and because of space’s elasticity, this creates ripples of space that spread out like ripples on a pond.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zLAmF0H-FTM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch the ripples until the black holes collide.</span></figcaption>
</figure>
<p>When the ripples pass pairs of masses, the rippling distortions of space cause the spacing between the masses to fluctuate in unison. But as an observer you simply see that the spacing between the masses is vibrating. It looks like a sound and it sounds like a sound! The only catch is that it needs to be amplified a billion times to be audible.</p>
<p>The first signal itself was detected as a vibration of the distance between mirrors four kilometres apart. They changed their spacing by about a billionth of the diameter of an atom. </p>
<p><audio preload="metadata" controls="controls" data-duration="11" data-image="" data-title="The sound of two black holes colliding." data-size="166960" data-source="LIGO" data-source-url="https://soundcloud.com/newyorktimes/the-sound-of-two-black-holes-colliding" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/320/ligo-chirp-1080p.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
The sound of two black holes colliding.
<span class="attribution"><a class="source" rel="nofollow" href="https://soundcloud.com/newyorktimes/the-sound-of-two-black-holes-colliding">LIGO</a><span class="download"><span>163 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/320/ligo-chirp-1080p.m4a">(download)</a></span></span>
</div></p>
<p>Sound carries a wealth of information. Think of the vast number of characteristic sounds we all know, from a dripping tap to a breaking window, from a bird call to a kettle drum. The sound describes the system. For gravitational waves we are able to make precise predictions of the differences in gravitational wave sounds from many systems. </p>
<p>The whoops and chirps we have heard are all different, because the sounds depend on the masses of the black holes, how fast they are spinning and how they are oriented relative to the Earth. Neutron stars are much less massive than the black holes we have heard so far, and this causes the pitch of the signal to rise much more slowly. </p>
<p>All the gravitational waves we have heard so far are in the audio frequency range for the human ear: we really could hear them if our ears were sensitive enough, but real signals are just too quiet.</p>
<p>In the future gravitational wave detectors in space will be able to listen to gravitational waves at much lower frequencies. These, like earthquakes, will need to be sped up for us to hear them.</p>
<p>Gravitational wave detectors are supersensitive microphones for the sounds of space. They amplify the sound, and we get to hear the sound of gravitational waves that have travelled to us from far away in the universe. The universe speaks to us.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a>
</strong>
</em>
</p>
<hr>
<h2>A better detector</h2>
<p>From the recent discoveries we can make predictions of what we might hear as we improve the detectors. As sensitivity improves you increase the range of detection and this increases the volume of the universe you can listen to by the cube of the improvement factor. </p>
<p>Every two times improvement gives eight times as many signals. In the next few years the three detectors in the world: two <a href="https://www.ligo.caltech.edu/">LIGO detectors in the US</a> and the <a href="http://public.virgo-gw.eu/language/en/">Virgo detector in Europe</a> should be detecting hundreds of black holes and neutron stars colliding every year. Two more detectors are under construction in Japan and India.</p>
<p>More detectors helps to pinpoint where signals come from, but the biggest pay off comes from increasing sensitivity. Just four-fold further improvement would expand our horizon to encompass about half of the visible universe while a ten-fold improvement would give us the whole universe. Detectors with this capability have been suggested for Australia, China, Europe and the US. </p>
<p>The legacy of Einstein, the <a href="https://theconversation.com/an-award-with-real-gravity-how-gravitational-waves-attracted-a-nobel-prize-66491">recent Nobel Prize winners</a> and the huge international team of gravitational wave physicists that made the first discoveries, will be the ability to listen to the whole universe, and to hear it running down as black holes form and grow.</p>
<p>Gravitational waves are truly a new sense for humanity. We are no longer deaf to the sounds of space. We can be pretty certain that our new-found sense will bring with it surprises and unforeseen revelations, as well as remarkable new technologies.</p><img src="https://counter.theconversation.com/content/92356/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council</span></em></p>From a slow hum to a chirp or a bleep, what is that sound you hear whenever there’s a new detection of gravitational waves?David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/889982017-12-12T14:42:56Z2017-12-12T14:42:56ZHow crashing neutron stars killed off some of our best ideas about what ‘dark energy’ is<figure><img src="https://images.theconversation.com/files/198773/original/file-20171212-9386-1cdozau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist s impression of merging neutron stars.</span> <span class="attribution"><span class="source"> Author University of Warwick/Mark Garlick</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>There was much excitement when scientists <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">witnessed the violent collision of two ultra-dense, massive stars</a> more than 100m light years from the Earth earlier this year. Not only did they catch the resulting gravitational waves – ripples in the fabric of spacetime – they also saw a practically instantaneous flash of light. This is exciting in itself and was the first direct evidence for a merger of neutron stars.</p>
<p>But from a cosmologist’s perspective, the photo-finish of the gravitational waves and the flash of light has at a stroke demolished years of research into a completely unrelated problem: why is the expansion of the universe accelerating? </p>
<p>It turns out that space and time are actually mutable, pliable, flexible and wiggly, rather than constant, fixed or immovable. This has been known since Einstein published his theory of general relativity, which explains how gravity warps spacetime. The subtle effects that this mutability causes need to be accounted for even in the GPS that makes your sat nav and iPhone work. </p>
<p>One prediction of Einstein’s theory was that it should be possible for spacetime to have waves in it, like the surface of the sea. These would be visible if one could, for example, smash together two black holes. This prediction was <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">dramatically seen</a> in the first detection of gravitational waves by the LIGO experiment in 2015. The discovery opened up a <a href="https://theconversation.com/experiments-simultaneously-detect-gravitational-waves-and-help-open-up-a-new-era-of-astronomy-84818">whole new way to probe the cosmos</a>, and was awarded the <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">Nobel Prize for physics</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=419&fit=crop&dpr=1 600w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=419&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=419&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=526&fit=crop&dpr=1 754w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=526&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=526&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Galaxy cluster SDSS – what’s pushing it apart at an accelerated rate?</span>
<span class="attribution"><span class="source">ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech).</span></span>
</figcaption>
</figure>
<p>The new detection of gravitational waves from the merger of neutron stars also has profound implications for our understanding of the universe. However for the cosmologists it was the flash of light 1.7 seconds after the gravitational waves that was the more intriguing observation.</p>
<h2>The cosmic speed camera</h2>
<p>The 1.7 second time delay is important because it means that the gravitational waves and the light waves had been travelling at almost <em>exactly</em> the same speed. In fact these are two of the most closely matched observed speeds ever: the two only differed by one part in 10m billion. </p>
<p>To put this into context if the speed cameras on the road could measure speed differences this finely you would get a ticket for going 30.0000000000000001mph in a 30mph zone. </p>
<p>Compared to the best measurements cosmologists were hoping for in the future this is a factor of a million billion times better. Factoring in that the electromagnetic waves may have taken a bit of time to escape from the turmoil of a neutron star collision, for all intents and purposes the speed difference is zero. </p>
<p>Cosmology is <a href="https://theconversation.com/cosmology-is-in-crisis-but-not-for-the-reason-you-may-think-52349">in a bit of a pickle</a>. We have a great model that can explain the evolution of the universe from a fraction of a second after the big bang, until now approximately 14 billion years later. The problem is that in order to explain all the observations, a mysterious energy called “dark energy” must be added to the models. Dark energy is a huge problem, it accounts for about 70% of all the energy the universe, and we have absolutely no idea what it is.</p>
<p>Dark energy is <em>like</em> an anti-gravitational effect that is pushing the universe apart and causing its expansion to accelerate. So to explain dark energy, cosmologists have attempted to change or replace Einstein’s theory to see if a new theory of spacetime could finally explain the effects of dark energy. </p>
<p>One way that cosmologists tried to do this was by changing the speed in which gravitational waves and light travelled. There were many different theories that had this component – each with a peculiar name like quartic and quintic galileons, vector-tensor theories, generalised proca theories, bigravity theories and so forth. Without data any of the theories could have been correct, and there were many people hopeful that they could be the next Einstein or Newton. </p>
<h2>Where are we now?</h2>
<p>But now in a single observation from a single neutron star merger a wide variety of these have now been consigned to cosmological dustbin in a flurry of papers (<a href="https://arxiv.org/abs/1711.09430">here</a>, <a href="https://arxiv.org/abs/1710.05901">here</a>, <a href="https://arxiv.org/abs/1712.02710">here</a>, <a href="https://arxiv.org/abs/1711.00492">here</a>, <a href="https://arxiv.org/abs/1710.06394">here</a> and <a href="https://arxiv.org/abs/1710.05893">here</a>). So no new Einstein yet.</p>
<p>In the absence of compelling data, it is still possible that we can update Einstein so we can account for dark energy. But the wiggles from the gravitational wave data has left very little wriggle room. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the finished square kilometre array.</span>
<span class="attribution"><span class="source">Swinburne Astronomy Productions for SKA Project Development Office</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>All the theories that have survived the pruning are much simpler than those that were allowed before; and the simplest theory, and the frontrunner, is that dark energy is the energy of empty space, and just happens to have the value we observe.</p>
<p>Another explanation that has survived is that it’s a Higgs-like field. The <a href="https://theconversation.com/nobel-prize-in-physics-goes-to-discovery-of-the-higgs-boson-19014">now famous Higgs boson</a> is a manifestation of a “Higgs field” – the first “scalar field” observed in nature. This is a field that has a value at every point in spacetime, but no direction. An analogy would be a pressure map on a weather forecast (values everywhere but no direction). A wind map, on the other hand, isn’t a scalar field as it has speed and overall direction. Apart from Higgs, all particles in nature are associated with “quantum fields” that aren’t scalar. But like the Higgs, dark energy could be an exception: a ubiquitous scalar field pushing the universe apart in every direction. </p>
<p>Thankfully we won’t have to wait long before <a href="https://theconversation.com/the-experiments-trying-to-crack-physics-biggest-question-what-is-dark-energy-52917">new telescopes</a> will test the remaining theories and a big piece of the cosmological puzzle will be completed.</p><img src="https://counter.theconversation.com/content/88998/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Kitching receives funding from the Royal Society and the Science & Technology Facilities Council.</span></em></p>Cosmologists who were hoping to be the next Einstein have had to bin their theories.Thomas Kitching, Reader in Astrophysics, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/861042017-10-24T20:18:24Z2017-10-24T20:18:24ZCosmic alchemy: Colliding neutron stars show us how the universe creates gold<figure><img src="https://images.theconversation.com/files/191637/original/file-20171024-30571-frs0vu.jpg?ixlib=rb-1.1.0&rect=96%2C0%2C803%2C573&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Illustration of hot, dense, expanding cloud of debris stripped from the neutron stars just before they collided.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">NASA's Goddard Space Flight Center/CI Lab</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>For thousands of years, humans have searched for a way to turn matter into gold. <a href="https://doi.org/10.1086/660139">Ancient alchemists</a> considered this precious metal to be the highest form of matter. As human knowledge advanced, the mystical aspects of alchemy gave way to the sciences we know today. And yet, with all our advances in science and technology, the origin story of gold remained unknown. Until now. </p>
<p>Finally, scientists know how the universe makes gold. Using our <a href="https://doi.org/10.3847/2041-8213/aa91c9">most advanced telescopes and detectors</a>, we’ve seen it created in the cosmic fire of the two colliding stars first detected by LIGO via the gravitational wave they emitted.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The electromagnetic radiation captured from GW170817 now confirms that elements heavier than iron are synthesized in the aftermath of neutron star collisions.</span>
<span class="attribution"><a class="source" href="https://www.caltech.edu/news/caltech-led-teams-strike-cosmic-gold-80074">Jennifer Johnson/SDSS</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Origins of our elements</h2>
<p>Scientists have been able to piece together where many of the elements of the periodic table come from. The Big Bang <a href="https://doi.org/10.1146/annurev.nucl.56.080805.140437">created hydrogen</a>, the lightest and most abundant element. As stars shine, they fuse hydrogen into heavier elements like carbon and oxygen, the elements of life. In their dying years, stars create the common metals – aluminum and iron – and blast them out into space in different types of <a href="https://doi.org/10.1146/annurev.astro.38.1.191">supernova</a> <a href="https://doi.org/10.1146/annurev-astro-082708-101737">explosions</a>.</p>
<p>For decades, scientists have theorized that these stellar explosions also explained the origin of the heaviest and most rare elements, like gold. But they were missing a piece of the story. It hinges on the object left behind by the death of a massive star: a neutron star. Neutron stars pack one-and-a-half times the mass of the sun into a ball only 10 miles across. A teaspoon of material from their surface would weigh 10 million tons.</p>
<p>Many stars in the universe are in binary systems – two stars bound by gravity and orbiting around each other (think Luke’s home planet’s suns in “Star Wars”). A pair of massive stars might eventually end their lives as a pair of neutron stars. The neutron stars orbit each other for hundreds of millions of years. But Einstein says that their dance cannot last forever. Eventually, they must collide.</p>
<h2>Massive collision, detected multiple ways</h2>
<p>On the morning of August 17, 2017, a ripple in space passed through our planet. It was detected by the LIGO and Virgo gravitational wave detectors. This cosmic disturbance came from a pair of city-sized neutron stars colliding at one third the speed of light. The <a href="https://doi.org/10.1103/PhysRevLett.119.161101">energy of this collision</a> surpassed any atom-smashing laboratory on Earth.</p>
<p>Hearing about the collision, astronomers around the world, <a href="http://kilonova.org/about.html">including</a> <a href="https://dabrown.expressions.syr.edu/">us</a>, jumped into action. Telescopes large and small scanned the patch of sky where the gravitational waves came from. Twelve hours later, three telescopes caught sight of a brand new star – called a kilonova – in a galaxy called NGC 4993, about 130 million light years from Earth.</p>
<p>Astronomers had captured the light from the cosmic fire of the colliding neutron stars. It was time to point the world’s biggest and best telescopes toward the new star to see the visible and infrared light from the collision’s aftermath. In Chile, the Gemini telescope swerved its large 26-foot mirror to the kilonova. NASA steered the Hubble to the same location.</p>
<figure>
<img src="http://kilonova.org/img/DECam_fading_kn_final.gif">
<figcaption><span class="caption">Movie of the visible light from the kilonova fading away in the galaxy NGC 4993, 130 million light years away from Earth.</span></figcaption>
</figure>
<p>Just like the embers of an intense campfire grow cold and dim, the afterglow of this cosmic fire quickly faded away. Within days the visible light faded away, leaving behind a warm infrared glow, which eventually disappeared as well. </p>
<h2>Observing the universe forging gold</h2>
<p>But in this fading light was encoded the answer to the age-old question of how gold is made.</p>
<p>Shine sunlight through a prism and you will see our sun’s spectrum – the colors of the rainbow spread from short wavelength blue light to long wavelength red light. This spectrum contains the fingerprints of the elements bound up and forged in the sun. Each element is marked by a unique fingerprint of lines in the spectrum, reflecting the different atomic structure.</p>
<p>The spectrum of the kilonova contained the fingerprints of the heaviest elements in the universe. Its light carried the telltale signature of the neutron-star material decaying into platinum, gold and other so-called <a href="https://en.wikipedia.org/wiki/R-process">“r-process” elements</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Visible and infrared spectrum of the kilonova. The broad peaks and valleys in the spectrum are the fingerprints of heavy element creation.</span>
<span class="attribution"><span class="source">Matt Nicholl</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>For the first time, humans had seen alchemy in action, the universe turning matter into gold. And not just a small amount: This one collision created at least 10 Earths’ worth of gold. You might be wearing some gold or platinum jewelry right now. Take a look at it. That metal was created in the atomic fire of a neutron star collision in our own galaxy billions of years ago – a collision just like the one seen on August 17.</p>
<p>And what of the gold produced in this collision? It will be blown out into the cosmos and mixed with dust and gas from its host galaxy. Perhaps one day it will form part of a new planet whose inhabitants will embark on a millennia-long quest to understand its origin.</p><img src="https://counter.theconversation.com/content/86104/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duncan Brown receives funding from the National Science Foundation and the Research Corporation for Science Advancement.</span></em></p><p class="fine-print"><em><span>Edo Berger receives funding from the National Science Foundation and NASA. </span></em></p>Until the recent observation of merging neutron stars, how the heaviest elements come to be was a mystery. But their fingerprints are all over this cosmic collision.Duncan Brown, Professor of Physics, Syracuse UniversityEdo Berger, Professor of Astronomy, Harvard UniversityLicensed as Creative Commons – attribution, no derivatives.